My character, a barbarian with the feat Improved Unarmed Strike,1 occasionally eschews his greataxe and punches monsters. After reading this 2009 thread and this 2009 thread, I don't know what works and what doesn't so that this barbarian's unarmed strike is considered, for example, a +1 brash (MIC 30) furious (OA 125) fury (HB 130) weapon.
What magic items can and should2 be used to add magic weapon special abilities to this barbarian's unarmed strike and why?
- The amulet of mighty fists (DMG 246)?
- The bracers of striking (Magic of Faerûn 155-6)?
- The necklace of natural attacks (Savage Species 58)?
- An item not listed here?
I'm almost certain the DM won't allow the barbarian to pay 300 gp for a masterwork unarmed strike suitable for turning into a magic weapon (this question and some of its answers notwithstanding), despite how well-intentioned and sound such reasoning may be. That dog won't hunt, so don't argue for that.
This barbarian won't have monk levels until very high levels,3 but it would be a shame if the barbarian acquired an item that granted these weapon special abilities for his unarmed strike only to have to replace the item granting them when he finally gained those monk levels, so if the item also works during a monk's flurry of blows, that'd be awesome.
1 Having taken the alternative class feature city brawler (Dragon #349 92), this barbarian only gets "the effects of the feat Two-weapon Fighting (PH 102) when fighting unarmed," so I'm pretty sure this means a magic gauntlet (PH 116, 117-8) or a magic ward cestus (Sword and Fist 70, 74) won't work with this class feature, but if an advocate can be found, that's cool.
2 That is, should from an optimization standpoint: the item requiring the smallest outlay of resources that nonetheless achieves the stated goal.
3 Actually, he'll have levels in the variant chaos monk (Dragon #335 89), which doesn't, in fact, get the special ability flurry of blows but the similar enough flailing strike.
Best Answer
If unconcerned with enhancement bonuses and only needing the weapon special abilities, the 1st-level artificer infusions personal weapon augmentation [trans] (Eberron Campaign Setting 117) et al. and personal natural weapon augmentation [trans] (Races of Eberron 188) et al. grant weapon special abilities to one of the creature's weapons or natural weapons.1 A wand of personal weapon augmentation (1st-level spell at caster level 1) (15 gp/charge) is inexpensive enough that even if adding the magic weapon special ability brash (MIC 30) to one's unarmed strike every encounter, that will still be cheaper than having such as permanent magic weapon special ability using the methods below. The magic weapon special ability furious (OA 125) is in a similar but worse position, as such an effect can only be granted by a wand of weapon augmentation [trans] (ECS 117) (4th-level spell at caster level 7) (420 gp/charge), likely making long-term use too expensive to use such an item to consistently have, for example, furious fists.
If the enhancement bonus is desired, an alternative is finding a way to cast the 4th-level Drd spell superior magic fang [trans] (SpC 136). This is a very expensive wand (a wand of a 4th-level spell at caster level 20 costs 1,200/charge), but that 60,000 gp item grants all of the creature's natural attacks a +5 enhancement bonus and, by the time such a wand can be afforded, the character probably won't be participating in 50 more fights during his career.2 Note that this also assumes the spell superior magic fang can affect unarmed strikes. (While the spell magic fang implies that spell can, the spell superior magic fang lacks such language.)
However, all these all run afoul of the opportunity cost needed to activate them, so I understand why you'd avoid them. Attempting to generate such effects faster makes the price higher and makes the options below even more appealing.
Let's do some math!
Amulet of Mighty Fists (DMG 246)
The amulet of mighty fists specifically improves both the wearer's unarmed strikes and the wearer's natural attacks, but only grants both enhancement bonuses on attack rolls and damage rolls.
Unfortunately, the amulet of mighty fists apparently can't grant the wearer's unarmed strikes and natural weapons magic weapon special abilities (that is, at least it can't without DM permission).
Bracers of Striking (Magic of Faerûn 155-6)
These cost 1,310 gp, weigh 1 lb., occupy the bracers slot, and grant the wearer the ability to make unarmed strikes as if the wearer possessed the feat Improved Unarmed Strike (very carefully not granting the actual feat). They can be made magical as if they were a blunt double weapon (hence any magical enhancement bonus or special ability costs double, the text implying that each "fist" (or head, I guess?) can't be magicked separately).
The item is not as explicit as it could be (the bracers can be modified with additional magic weapon special abilities but don't say those affect the wearer's unarmed strike, and I've read at least one argument wherein it was said seriously that the bracers' themselves must be used to beat a fool to employ their weapon special abilities), but if one assumes the enhancement bonuses apply to unarmed strikes and one's only making unarmed strikes, the bracers are a better deal than the amulet of mighty fists.
Necklace of Natural Weapons (Savage Species 58)
This item affects but a lone natural weapon unless more cash is paid. It's acknowledge that unarmed strikes are not natural weapons (but there's a counterargument couched in the fanged ring, below), so this probably doesn't do you any good, but it's included for completeness because you asked. The cost is multiplied by the number of natural weapons the amulet affects.
This makes the necklace of natural weapons a better deal than the amulet of mighty fists only if the wearer has but one or two natural weapons, except that the necklace explicitly can have magic weapon special abilities, and the DM must approve the idea that magic weapon special abilities can be added via the amulet.
Other Options
Below are a few options unmentioned by your question.
"So what do I buy?"
If you're using only unarmed strikes, you'll need the bracers. Fortunately, some of the weapon special abilities you want only require the weapon to be wielded, so, for example, you could get the following:
And if, for example, you bind the soulmeld girallon arms (Magic of Incarnum 68) to your totem chakra and want magic weapon special abilities for that soulmeld's four claw attacks, you'll need the necklace.
Note: The magic weapon special ability fury (HB 130) (+1 bonus; 0 lbs.) needs to apply to every natural weapon and unarmed strike for it to be worthwhile, yet the special ability deals but an extra +1d6 points of damage (albeit untyped) each and only while raging, so, really, I suggest just skipping that magic weapon special ability. The same and more goes for the weapon special ability berserker (MIC 29) (+1 bonus), and more being that the weapon special ability is limited to two-handed weapons (which, with an inappropriately large magical ward cestus, is a possibility but a silly and impractical one).
Other Useful Items
1 Fortunately, the infusion personal weapon augmentation targets but a weapon and its description only mandates it affect a weapon, saying nothing about the weapon being manufactured, so affecting an unarmed strike should be a thing even if not a monk.
2 This overstates things a little. The character'll probably need to buy two or even three eventually. Each wand contains sufficient charges to use 1 charge per encounter for about 3 levels worth of encounters. A third wand tips things in favor of the amulet over the course of the character's career.