First of all, the Prestige Class Tier List is not nearly as widely-ascribed-to as JaronK’s base class one. For one thing, it is much harder to judge a prestige class (especially ones that can vary so much depending on how you enter), and for another there are just so many more of them.
Take the Shadowsun Ninja. For a Monk, it’s a dramatic step up; for a Swordsage, it’s... a thing. There are some neat tricks possible with it (Tomb-Tainted Soul or the Undead type allow you to use the negative energy for healing while using the positive energy on your allies, so that’s indefinite healing), but ultimately it doesn’t really change much about the Swordsage’s tier.
The problem of the Master of Nine is that it requires a ton of feats. If you aren’t a Swordsage, it also requires multiclassing, but that’s not really a bad thing for initiators. In fact, judicious multiclassing helps a great deal with the feats, because one level in Cleric gets you two of the feats (Darkness or Shadow domain gets Blind-fight, Time domain gets you Improved Initiative). The unarmed Swordsage adaptation also gets you Improved Unarmed Strike, and most Swordsages want Adaptive Style anyway.
That leaves only Dodge to be picked up. Several options, including Tome of Battle’s own Desert Wind Dodge, are better than ordinary Dodge, though even the best is still weak. Still, one feat burned and the single-best-dip-in-the-game (don’t forget that Cleric 1 also gives a few spells, and Turn Undead can be used to fuel the often-excellent [Divine] and [Domain] feats) is not too high a price to pay for the excellent class features that Master of Nine offers.
The limited Dual Stance feature is not nearly as good as the Warblade’s version of the same, but it’s still awesome and you can get it way sooner than 20th level. The eight maneuvers in five levels, of course, is phenomenal, and a maneuver readied per level is insane.
If you try to get into Master of Nine as a regular, single-classed Swordsage, you’re making a huge mistake and will regret burning all of your feats that way. If you’re clever about picking up feats, though... the class can be excellent.
Side-note: you don’t lose “more” by taking another level in addition to Cleric 1 with your Swordsage levels, because other class levels count half for your initiator level. There are a lot of great options for that extra level. Fighter or Psychic Warrior could be used to get another feat, to make up for the one lost picking up (Desert Wind) Dodge. Psychic Warrior also grants you a single power – which could be expansion, for instance, a great choice. Barbarian gives a ton of stuff on level 1 as well (don’t forget to check the various alternatives for Rage for the one that best works for you).
Now that the Advance Class Guide is out, the answer has changed (as @Lord_Gareth suggested it would in his January 2014 answer).
And now that the ACG errata is out, the answer has changed again. Changes incorporated below.
As of today, there are two published feats (three if you include Mythic) that expand the set of finesse weapons:
1. Dervish Dance
(which requires a 13 DEX, Weapon Finesse, 2 ranks in Dance, and proficiency in the scimitar) lets you count a scimitar as a finesse weapon (and add DEX instead of STR to damage)...as long as it's sized for you, used one-handed, and you aren't "carrying a weapon or shield in your off hand."
2. Slashing Grace
(which requires a 13 DEX, Weapon Finesse, and Weapon Focus) lets you use DEX (instead of STR) for damage with any one handed or light slashing weapon one has Weapon Focus in. As with Dervish Dance the weapon has to be sized for you. Additionally (since the errata)
You do not gain this benefit while fighting with two weapons or using flurry of blows, or any time another hand is otherwise occupied.
Note though that it doesn't allow one to use DEX to hit with a one-handed slashing weapon unless one has at least 1 level in swashbuckler. Swashbuckler's get the Swashbuckler's Finesse ability which says:
a swashbuckler gains the benefits of the Weapon Finesse feat with light or one-handed piercing melee weapons.
That combined with this text from Slashing Grace:
When wielding your chosen weapon one-handed, you can treat it as a one-handed piercing melee weapon for all feats and class abilities that require such a weapon
lets swashbucklers (but not others with Weapon Finesse) use DEX to hit with a longsword or similar weapon. (A fighter with Weapon Finesse and Slashing Grace gets DEX to hit with her rapier but still uses STR for damage. If she switches to a longsword she gets DEX to damage but is back to using STR to hit.)
Also note (as per the original question) that Slashing Grace makes a bastard sword a finesse weapon for swashbucklers...but only while wielded one-handed.
Bucklers and Swordsmaster's Flair are OK!
The following FAQ was asked about Slashing Grace but applies to Dervish Dance as well.
What exactly does it mean that “You do not gain this benefit while fighting with two weapons or using flurry of blows, or any time another hand is otherwise occupied?” Can I use a shield? What about a buckler? Can I use flurry of blows? Brawler’s flurry? Two-weapon fighting? Spell combat? Attack with natural weapons? What if I throw the weapon? What about swordmaster’s flair?
Slashing Grace does not allow most shields, but bucklers work because they don’t occupy the hand. Flurry of blows, brawler’s flurry, two-weapon fighting, and spell combat all don’t work with Slashing Grace. Attacking with natural weapons beyond the weapon you chose for Slashing Grace also does not work. Slashing Grace only works with melee attacks, not thrown attacks with a melee weapon. Swordmaster’s flair should have a sentence added to it that says “Carrying a swordmaster’s flair counts as having that hand free for the purpose of abilities that require a free hand, though you still can’t hold another object in that hand.”
Why No Love For Rapiers?
As an aside, Jason Bulmahn (Lead Designer) has said that DEX to damage was a late addition to Slashing Grace, and the design team didn't realize that it made a longsword significantly better for a swashbuckler than the more iconic rapier. To solve that, they've announced that the following feat will be released in the upcoming Pathfinder Player Companion: Advanced Class Guide Origins:
FENCING GRACE (COMBAT)
Your extreme style and fluid rapier forms allow you to use agility rather than brute force to fell your foes.
Prerequisites: Dex 13, Weapon Finesse, Weapon Focus (rapier).
Benefit: When wielding a rapier one-handed, you can add your Dexterity modifier instead of your Strength modifier to that weapon’s damage. The rapier must be one appropriate for your size.
In addition, if you have the panache class feature, you gain a +2 bonus to CMD against attempts to disarm you of your rapier while you have at least 1 panache point.
Mythic note: one more way to get DEX to Damage
While the core of this question is about adding to the set of finesse weapons, both Slashing Grace and Dervish Dance also add DEX to damage (arguably their bigger benefit). For completeness, I'll add one more DEX to damage option: Mythic Weapon Finesse.
If you happen to be playing with the optional Mythic rules, this is generally the best solution. The Mythic Weapon Finesse feat's only requirement is that you already have the general Weapon Finesse feat. It states,
When using Weapon Finesse, you may also use your Dexterity modifier instead of your Strength modifier on your damage rolls.
So (unlike the options above, you can use any shield, flurry of blows, all of your natural attacks, etc.). It even tacks on the further benefit that > If you carry a shield, its armor check penalty doesn't apply to either the attack rolls or the damage rolls.
Best Answer
There are a very, very few features of legacy items that are not generally available on non-legacy items. The overwhelming majority of legacy abilities are quite common on magic items (bonuses to attack, AC, damage, saving throws, skills, etc., spell effects, metamagic rod effects), but these few, at least, are things you wouldn’t be able to just get somewhere else. Anything you could get from a non-legacy item is better gotten from a non-legacy item, as the personal costs of legacy items are prohibitive.
Note that things from the legacy ability menus are available either by founding your own legacy, or through the legacy champion’s ability to replace legacy abilities, but the latter can only ever access menus A, D, and G.
Creature Compass (Least, legacy ability menu A [chosen as with ranger favored enemy], Bloodcrier’s Hammer 6th [earth], Bow of the Black Archer 5th [drow])—This allows you to “detect” creatures of a particular type or subtype, and ignore the DR of such creatures. Exceedingly niche, but for many creature types there are no corresponding detect spell, so it’s at least unique. Unfortunately, what exactly “detect” means in this context is not explained, so it could range from the decidedly-mediocre (aware of presence, but not number or specific location) to the quite-good (able to pin-point them exactly and ignore any concealment they may have, even see them through walls within the range). Ask your DM where it actually lands, though keep in mind that no matter how good it actually is, burning your standard action concentrating on it really limits your ability to use that information.
Cunning (Lesser, legacy ability menu D, Mau-Jehe 13th)—Immunity to being flat-footed? That’s actually seriously good. If you can either found a legacy or take enough levels of legacy champion to replace one of your legacy item’s abilities with this, that alone could go a long way to justifying unlocking at least that many abilities. The presence of this ability on Mau-Jehe is kind of interesting, too, since Mau-Jehe has a couple other features that are also unique, and one can almost imagine Mau-Jehe being worth it if one imagines a world where soulknives didn’t suck. Unfortunately, that’s not the world of D&D 3.5.
Intelligent Legacy (Least, legacy ability menu A, Ur 5th; Lesser, legacy ability menu D, Exordius 12th, Flamecaster’s Bolt 11th, Ur 11th, Wargird’s Armor 12th; Greater, Ur 17th)—Intelligent non-legacy items exist, but aside from this legacy feature, there isn’t really any way for a player to ensure that his character finds one. Intelligent items potentially have a lot of benefits, but the inability to customize legacy items makes it difficult to truly take advantage of here. Ur’s intelligence is interesting just for being so much earlier than the others.
Pathbreaker (Least, Bloodcrier’s Hammer 7th)—It opens things. Once per day. It’s slightly better than knock (it can permanently open things under arcane lock rather than just opening them for 10 minutes), but only very slightly (and even then I can imagine preferring knock in some situations).
Giant Bearing (Lesser, Bullybasher 13th)—You kinda-sorta grow a size category, but you miss out on reach which is easily the best feature of growing. Still, it stacks with actual size increases (aside from the awkward ability to grapple Huge creatures, which as-written applies literally to only Huge creatures regardless of your size) as well as with powerful build, so that’s... something.
Stone Gathering (Lesser, Bullybasher 15th)—You can throw large-ish rocks, and catch the same. It’s really not impressive for 15th level. Go hulking hurler if you really want this.
Frightful Presence (Greater, Bullybasher 17th)—I’m sure there are vastly easier ways to get it, but I’m less sure there are items with it. Still isn’t worth it even if so.
Unstoppable Cleave (Lesser, Caladbolg 15th)—Caladbolg is seriously an insult to the name, but anyway, this allows you to, once per round, keep going with Great Cleave even if you fail to drop an opponent. Note that Caladbolg does not actually grant Great Cleave, so that would be something you’d have to spend feats on to even benefit here.
Devious Mastery (Least, Devious 6th)—Always able to take-10 on Bluff checks to verbally deceive someone, which is most Bluff checks.
Vicious Mastery (Least, Vicious 6th)—Always able to take-10 on Intimidate checks to demoralize an opponent, which is popular enough as a tactic.
Pelor’s Dazzling Beneficence (Greater, Durindana 19th)—15 rounds/day of total concealment that you can turn on as a swift action doesn’t entirely suck, though by 19th level I have serious doubts about it really changing anyone’s life much.
Deflect Attack (Least, Dymondheart 6th)—1/day, negate any ranged attack, explicitly including magic attacks like rays. The 4th-level bard/sor/wiz spell ray deflection is vastly superior, but this is technically available before that.
Whip Wrap (Least, Flay 8th)—You can grapple someone with Flay and then let it go, allowing it to continue grappling on its own. It even has some constrict damage. Of course, this sounds like an excellent way to lose the incredibly-dear legacy item you have invested so much in, so even though the effect is quite decent, the risk is just astonishing.
Storm Vision (Least, Frostburn’s Wrath 6th)—Reduce the amount that rain, snow, and sleet hamper your vision. I actually strongly suspect that there are items to do this but I don’t know of any off the top of my head. Not a terrible effect on its own but not worth the price of admission.
Wolfsbane (Least, Full Moon’s Trick 5th)—Eliminate any form of shapeshifting or polymorph on hit, at will. DC is only 15, which means this isn’t exactly super-great, but it could mess with someone’s plans quite a bit if it works.
Automatic Writing (Lesser, Ghostfolly’s Gloves 12th)—Massively late in the game for such an effect, but being able to take snapshots of writing, illustrations, diagrams, and so on is pretty useful. Not, ya know, worth it, particularly with the 1-page-at-a-time limit, but I could see wanting the ability if it were available sooner and at less cost.
Magefinder (Least, Hammer of Witches 5th)—The wording on this ability implies that the Hammer of Witches glows in the presence of arcane spellcasters even without unlocking it, but I cannot actually find this in the write-up. Thus, I’ll stretch things a bit and give magefinder credit with that ability. Useless if you travel with any arcanists, but if you don’t, lighting up when an arcane spellcaster is around could be invaluable if they’re sneaking or hiding their nature. The at-will detect magic, which is supposedly the real benefit of magefinder, is meh.
Axe Casting (Least, Lorestealer 6th [up to 3rd-level spells]; Lesser, Lorestealer 13th [up to 6th-level spells])—Once per day (twice at 16th), you can chop a scroll with Lorestealer to cast it. Which is kind of hilarious and silly. Ultimately, though, Use Magic Device or just dipping a spellcasting class is just vastly superior to Lorestealer; if nothing else, that lets you use wands, and wands are much better than scrolls.
Knife Made Mind (Least, Mau-Jehe 5th)—You can make Mau-Jehe a mind blade, which is pretty unique. If you are a soulknife, your soulknife class features that improve mind blades explicitly stack with the benefits of Mau-Jehe, which... would be pretty decent if only soulknives didn’t suck to begin with ⌐.⌐
Stable Focus (Least, Mau-Jehe 9th)—For one psionic feat of your choice, you are always considered to have psionic focus. Which isn’t entirely awful, but at this cost it should just apply to everything.
Sense Alien (Least, Planeshifter’s Knife 5th)—At-will detect evil but for all extraplanar creatures. Creature Compass [extraplanar] is clearly superior, but this is unique...
Reality Slice (Least, Planeshifter’s Knife 9th)—Confirming my suspicion that Planeshifter’s Knife was a thinly-veiled reference to Philip Pullman’s subtle knife, this ability allows you to use rope trick without the rope. Considering that you can just pull the rope up with you when you use rope trick, that doesn’t seem like much of a bonus to me, but oh well, it is unique.
Planar Cunning (Lesser, Planeshifter’s Knife 13th)—The excellent cunning ability, but limited only to extraplanar creatures. Lame.
Painless Spur (Least, Quickspur’s Ally 9th)—Spur a mount without damaging it. If, like me, you forgot that spurring a mount even dealt damage, we’re talking about 1 damage dealt to add 10 feet to the mount’s movement speed for a round, but the damage doubles each consecutive round you spur the mount. Seems to me that you really shouldn’t need to spur your mount that much, but I guess it’s something. Something easily replaced by just getting your mount a bonus to its movement speed, but whatever.
Eye of Mortality (Least, Scales of Balance 6th)—A 1-round detect effect that determines if a creature is 1. living and mortal, 2. living and immortal, 3. undead, or 4. construct. Replaced for the most part by just having some Knowledge skills.
Lion’s Charge (Greater, Shishi-O 17th)—Pounce. At 17th.
Stunning Stone (Least, Sling of the Dire Wind 5th)—Works like the Stunning Fist feat, except armed and at range, and fixed at 3/day.
River of Plenty (Least, Staff of the Torrent Moons 9th)—3/day create holy water for free if you are Good. It will take a very long time for that ability to produce a return on investment...
Adjustable Draw (Least, Stalker’s Bow 5th)—Add Strength bonus to damage, as if Stalker’s Bow was composite and set to exactly your Strength. Not wholly unique, but it is rare and most importantly, you do not need to pay any personal costs to get it.
Deadly Sniper (Least, Stalker’s Bow 10th)—3/day, reroll a critical confirmation roll against a flat-footed target. Have to decide to use it before the DM declares the original roll a success or failure. So we have an incredibly niche ability, that you may very well waste entirely, on a weapon with a 20/×3 critical stat, that for reasons unknown has to be limited to 3/day.
Crush the Weak (Least, Stormchaser’s Cudgel 10th)—Double threat range, explicitly stacking with Improved Critical or what have you. Would be decent if it could be applied to any weapon with fancy critical properties, but it’s a greatclub, so all it does for you is change your 20/×2 to 19-20/×2. Just using a 19-20/×2 weapon to begin with would be just as good.
Aberrant Sustenance (Least, Thanifex 5th)—Whenever Thanifex kills something, the wielder does not need food or drink for the next 24 hours, and the victim needs resurrection or better to be revived. In a low-level setting, that could be powerful as other sources of blocking raise dead might be out of reach. And there are no personal costs to get it.
Green Empathy (Least, Treebrother 6th)—Wild empathy, but for plants. Unique, but shockingly pointless.
Woodland Stealth (Least, Treebrother 10th)—Hide in plain sight if you are in the same square as a tree. Joy?
Savage Transformation (Greater, Ur 20th)—Once per day, for 10 rounds, you simply ignore any damage that would reduce you to negative HP. You’re also immune to fear, poison, or death effects. Unfortunately, you also cannot heal, so you’d spend a lot of time disabled if it came down to that, but that’s still better than dead. Plus there may be ways to not be disabled at 0 HP, which makes this way better. A legacy champion could also get extra uses of this.
Fiery Blade (Lesser, Desert Wind [ToB version] 12th)—If you don’t know burning blade, you can initiate it 3/day, which is kinda-sorta interesting if only because that means you can use it multiple times in one encounter. More interesting is if you do know it, because then you get to initiate it as an immediate action. How on earth that works (considering burning blade’s duration of “the rest of your turn”) is anyone’s guess, but it is unique.
Boundless Determination (Lesser, Faithful Avenger 16th)—Either learn immortal fortitude, or if you already know it, add a decent chunk of temporary HP that refreshes every round to the stance.
Resiliency (Greater, Faithful Avenger 20th)—1/day, ignore damage from a single source. Uh, yeah, that could be very good. Though at 20th, you can definitely do better.
Intimidating Strike (Least, Supernal Clarity 5th)—Use sapphire nightmare blade 5/day, or if you already know it, add a +2 bonus to the Concentration check made during it.
Psychic Poise (Least, Supernal Clarity 8th)—3/day, use Concentration instead of Balance.
Uncanny Dodge (Lesser, Supernal Clarity 13th)—Can you get uncanny dodge from an item? I’m not sure you can, outside of this. Not that it would be remotely worth it.
Steel Wind (Least, Kamate 5th)—5/day use steel wind, or if you already know it, +1 to your attack roll when using it. Yawn.
Accurate Strike (Least, Kamate 9th)—3/day, ignore a foe’s concealment or even their incorporeal status for one attack as a swift action. Also a +4 bonus on any critical confirmation rolls for that attack, not that that is all that interesting.
Baffling Defense (Lesser, Eventide Edge 11th)—Learn comet throw (and not baffling defense, despite the name), or if you already knew it, +2 bonus on the touch attacks made initiating it.
Evasive Defense (Lesser, Eventide Edge 14th)—3/day, auto-succeed on the Sense Motive check made when using baffling defense (assuming you have it, since the baffling defense legacy ability doesn’t actually grant it) against foes larger than you.
Shadowcloak (Least, Umbral Awn 5th)—In the first round of an encounter, you can Hide from a flat-footed foes as long as you are within 10 feet of cover or concealment. Yay? Way, way too many caveats on this.
Sneak Attack (Least, Umbral Awn 8th)—Gain sneak attack from an item; I think that’s unique. Plenty of weapons can improve sneak attack, but gaining it is different.
Shadowhand (Least, Umbral Awn 10th)—If someone provokes an attack of opportunity from you while you are unarmed but have Umbral Awn available, draw it as an immediate action and take the attack of opportunity. The provoking opponent is considered flat-footed against the attack. Which is nice-ish, if niche as anything.
Shadowstep (Greater, Umbral Awn 20th)—3/day, swift action incorporeality for a turn. Nnnnot exactly amazing for 20th, but I can’t think of other items that will do it.
Frenzied Charge (Least, Tiger Fang 5th)—1/day, get an extra attack at the end of a charge.
Claw of the Tiger (Least, Tiger Fang 6th)—You cannot be disarmed of Tiger Fang and do not drop it when panicked or stunned.
Vicious Attack (Lesser, Tiger Fang 14th)—Increases the critical multiplier of Tiger Fang to ×3, which is notable since Tiger Fang is a kukri and so has a critical threat range of 18-20. There are not a whole lot of ways to get an 18-20/×3 weapon.
Devastating Attack (Greater, Tiger Fang 20th)—And now Tiger Fang is an 18-20/×4 weapon. Not wholly unique, but definitely rare. Certainly not worth it but oh well.
Leading the Attack (Least, Blade of the Last Citadel 5th)—5/day leading the attack or +1 to attack rolls with that maneuver if you already know it.
And that’s it for unique effects. A fairly lengthy list, but most of them are garbage, at least compared to when you get them and how much you have to pay for them. The cunning ability is the only one that catches my eye, really.
So honestly the best use I can think of here is some campaign using a fixed soulknife that’s actually good, and then using Mau-Jehe. Which doesn’t involve houserules to fix legacy items, but does definitely involve houserules.
Other than that, using Ur and abusing intelligent items somehow, and then maybe pulling some kind of crazy damage-echo shenanigans with its 20th-level feature, maybe? Don’t know how exactly you would manage to do it and it would only maybe work anyway.
Notably, the best unique legacy effects are creature compass, cunning, and intelligent legacy, which are all available when founding your own custom legacy, and furthermore are from legacy ability menus that the legacy champion can use to replace legacy abilities. So that’s something. You could argue that the best possible legacy weapon is like, one slot of intelligent legacy, four slots of creature compass, and then cunning and then as little else as possible to keep personal costs down. With such a weapon, you would probably never actually draw it, though.
For use as a weapon... none of these are great as a weapon. Founding a legacy is definitely the top route for that, because then at least you get actually-decent special weapon properties. But for that you could just buy a weapon.
Also, you might notice that basically none of the greater legacy abilities are worth a damn. The Ur capstone is about the only really interesting one. Faithful Avenger has a decent capstone, though in a lot of ways it’s a lesser version of Ur’s (and sweet jesus who thought taking a −10 penalty to Fort was viable?). Crit-fishers might be tempted by Tiger Fang but it’s really not worth it. So not performing the greater ritual is very strongly worth considering, no matter how much you want to utilize Weapons of Legacy.
Finally, the last trick I can think of is attempting to avoid advancing Stalker’s Bow and just using the auto-scaling Strength feature. Which is pretty garbage, considering that would prevent you from improving your weapon in any meaningful way, plus you would be forced to never again gain 3 skill points at a time so you can never pay the personal costs to advance it (advancing a legacy weapon is non-optional if you are capable of paying, at least until it comes time to do the next ritual, so you have to stay incapable). Even if you got it to work, it’s explicitly not the sort of thing you were looking for.
You could do a similar trick with Vicious, grabbing the skill mastery for demoralizing an opponent (which costs 2 HP in personal costs), and then if you never again gain 3 skill points at a time, you don’t advance Vicious any further. Of course, at that point you’ve just got Vicious in a sheath somewhere and that’s it. But certainly nothing else on Vicious is worth the costs. And the restrictions on the classes you can take to avoid advancing it are such that it doesn’t seem at all worth it. You’re almost-certainly better off dipping exemplar or something.