classdnd-3.5enon-combat
The common, D&D 3.5 fighter is a war machine, it is build to fight (effectively or not is another thing). But when it comes to out of combat situations, it's better built in technique to handle things is intimidating others.
So, aside from house-ruling more class skills and/or skill points, is there a class that has a good to great fighting potential, and can be useful in out of combat situations?
If you want to give your fighter more access to magic without rebuilding you're going to be limited to skills, feats, and magical items. None of these will give your fighter heavy magical abilities, instead letting you play the character as someone who has learned basic magic.
Skills
The skills that increase magical knowledge are:
Knowledge (Arcana) - represents general knowledge your fighter has acquired about magic; what an arcane symbol means, how the local mage guild heirarchy is organized. Stuff he would learn in school or from talking to spellcasters.
Spellcraft - much more specialized knowledge about specific magical effets. While Knowledge (Arcana) is theoretical studies, this is applied studies. Being able to recognize magical effects, figure out what spells are being cast. Knowledge gained by seeing magic in action, how it's been used.
Use Magic Device - knowing how to use the magical items that are common to spellcasters; staff, wands, scrolls, etc. The Evil Necromancer has defeated the parties fighter and is now monologuing to the rest of the party about their imminent defeat. The tired fighter rolls over, grabs the wand of fireballs from the necromancers belt and make a brilliant quip as fire blossoms around them.
Feats
There aren't a lot of feats that contribute to magical abilities. The first one I recommend is Able Learner from Races of Destiny. This feat treats all skills as being in-class skills. This will allow you to level up the above skills quicker.
The other feat that is useful is Magical Training, from the Players Guide to Faerun. It allows your character to cast three 0-level arcane spells per day as either a wizard or sorcerer.
Items
Have your character carry around magical items that are commonly associated with spellcasters. Staves, scrolls, wands. Combined with Use Magic Device this allows the fighter to have access to magical abilities.
A staff is an excellent choice of a magical item for this type of fighter. They can use it as their melee weapon, and use the magical abilities within it. A great surprise tactic when fighting: thrust, thrust, parry, Cone of Cold.
I try to avoid taking more than 3 levels of swashbuckler (insightful strike is its best feature) or 2 levels of fighter (a feat per level is OK; a feat every other level is pretty weak). I’d say it’s probably a good time to leave those classes behind.
The exception is if you take, e.g. Daring Outlaw (see below) to improve these classes. The Zhentarim Soldier ACF can also do wonders for the fighter class (up to 9th level anyway) if you have the Charisma and Intimidate ranks for it.
Just for the sake of anyone else reading this, the warblade (Tome of Battle) is perfect here: he’s flashy, highly-skilled, and makes good use of Intelligence (and he gets 4+Int skills). White Raven makes him an excellent battlefield leader.
(I just noticed you don’t have factotum listed either; that’s a real shame. Again, leaving this here for future users who do)
Factotum (Dungeonscape) sounds really perfect for your character here. They do gain a few spells (and some Supernatural abilities), though there are homebrew variants that can remove them. More importantly, the factotum’s whole schtick is “I add Intelligence to everything.” Like all Strength and Dexterity skill and ability checks (e.g. Athletics, Acrobatics, Stealth, Initiative) at level 3. In fact, the only notable thing that factota don’t add Intelligence to is damage: that you already have from swashbuckler’s insightful strike.
And a factotum is always the man with the plan, even if he’s actually just making it all up as he goes along. Seems like a pretty good guy to follow.
See this question for more information on using the factotum class well.
You may qualify for the chameleon prestige class (Heroes of Destiny or here) based on Able Learner (depends on whether or not you’ve been putting points in the skills you need). While the best feature of chameleon is their spellcasting options, you don’t need to use them. Two levels of chameleon gets you the wonderful “floating feat,” a feat you can change every day. A third level can get you some sneak attack damage, which is useful (see below re: Daring Outlaw).
This prestige class (Complete Scoundrel or here) isn’t very good and is probably way too specific for you: you want to be a leader of men, not hiding behind constantly-changing masks. But if you take just one level (i.e. only get one mask), and choose the gladiator mask, you get to be Maximus. You become proficient in every weapon ever, which is pretty awesome, and we all know how Maximus leaves everyone entertained.
The dread commando prestige class (Heroes of Battle or here) is full-BAB and gets sudden strike, which is the weak version of sneak attack (and stacks with sneak attack for qualifying). Requires Dodge and Mobility, which is a shame since they’re pretty weak and you should have ranks in Tumble to avoid AoOs anyway. Mobility, at least, can be gotten as an armor special ability (and the rules do allow you to qualify using items, but make sure DM allows it), but it’s quite expensive for your level.
Note that there are several feats (Midnight Dodge from Magic of Incarnum, Expeditious Dodge from Races of the Wild, Desert Wind Dodge from Tome of Battle) that count as Dodge and are better. Still not good, but better. Worth considering.
Anyway, dread commandos are skilled fighters, and the bonus damage is good for a finesse build, and you get some team-based bonuses. So fitting. But it’s a weak form of bonus damage and the team bonuses are pretty small, so not very good.
Bards require ranks in Perform, but unless you use their spells they don’t actually need Charisma. Just one level for inspire courage would not be a bad idea for the sake of being all leader-y. You can just ignore the cantrips that you get.
See this question for thoughts on making the most of the bard class.
Knight (Player’s Handbook II or here) is heavily-armored and full-BAB, and makes some solid attempts to protect others (e.g. test of mettle). Unfortunately, the knight’s code is extremely strict, even stricter than the paladin’s in a lot of ways.
It’s often said that knight has five good levels: 1, 2, 3, 4, and 20. If you go for knight, test of mettle and bulwark of defense are probably your best bets.
Instead of rage (or ferocity or whirling frenzy, which are probably more appropriate to you), call it something else: In the Zone, Focus, something. Refluff it as bullet time or something; the mechanics still work for that (particularly ferocity or whirling frenzy, which actually do make you move faster). One level in barbarian gets you these great features, and if you have Complete Champion available, you can also swap fast movement for pounce via the lion spirit totem alternate class feature, which is a great deal.
This doesn’t directly impact leadership skills, but it gives you a lot of martial prowess to back up your leadership.
If you already have very-high Charisma (16-18 before items), marshal (Player’s Handbook II) is worth it for the minor auras that add that to various things. But since you can change your minor aura whenever you like, and the major auras are weirdly weak, I don't think you need more than one level.
Legendary leader (Heroes of Battle) gives some solid abilities on an OK chassis. The problem is that it depends on the DM using the Commander rules found in Heroes of Battle, and in my experience, most don’t. Without them, a couple of abilities don’t really make sense.
If you do go this route, note that Iron Will can be bought for 3,000 gp (Otyugh Hole, Complete Scoundrel). Many DMs won’t allow it, but it’s definitely worth asking if you can. 3,000 gp is a bit much for a +2 bonus to a single save, but as something that counts for prerequisites, it’s a steal.
The Daring Outlaw feat (Complete Scoundrel) stacks your swashbuckler and rogue levels for grace and sneak attack. You need 2d6 sneak attack damage to qualify, which means three levels in rogue, or a level in rogue and a level in something else that gives sneak attack (or an analogue like the ninja’s sudden strike or the scout’s skirmish; both from Complete Adventurer).
Note that a dread commando (above) could take Daring Outlaw because sudden strike stacks with and counts as sneak attack for prerequisites. This will give you +2d6 sneak attack dice from swashbuckler levels, which is nice, and allows you to consider going back to swashbuckler for more.
It stacks swashbuckler and fighter, two classes you already have, which makes it seem appropriate, but they only stack for the purposes of grace and qualifying for fighter-only feats. With the exception of Weapon Supremacy (Player’s Handbook II, requires Fighter 18), the fighter-only feats are pretty weak, and grace isn’t too great.
If you have Knowledge skills, it’s an attack and damage bonus. Just worth mentioning because it’s a good feat that might fit the character. Depends whether or not your wit is backed up by real knowledge, though, since Knowledge Devotion does require a fair amount of, ya know, devotion to knowledge.
I like Barbarian 1, Bard 1, Chameleon 2, and Master of Masks 1 best of the options presented that are on your list of legal material. I wouldn’t take more levels of any of these classes, however. That gets you to 10th-level, anyway. After that, I suppose dread commando and/or legendary leader are probably your best bets.
The other option is to not bother with any of that hodgepodge and just go Swashbuckler 13/Fighter 2/Dread Commando 5 with Daring Outlaw. That gets you full BAB, 7d6 Sneak Attack, and 3d6 Sudden Strike. Of course, that assumes you can get Dodge and Mobility... Anyway, it will make you a reasonably effective melee combatant and give some minor bonuses to those around you. It’s not the best build available but it does have a certain elegance.
If you can get it allowed, I have to mention again how perfect warblade is here. With a start of swashbuckler 3/fighter 2, you can do really well by taking three other classes, and then taking warblade at 9th to start with an Initiator Level of 5, thereby starting with 3rd-level maneuvers and stances. My preferences for those three levels would be Factotum 3, Chameleon 2, Barbarian 1, Master of Masks 1, and/or Bard 1 (such that they add up to three, of course). For bard, Song of the White Raven becomes your obvious choice as 9th-level feat.
Best Answer
Depending on what supplements you want to consult there are quite some alternatives for a "fighting man" that have some more utility in and out of combat.
Generally speaking, the classes from the Book of Nine Swords - especially the Warblade! - are generally better and more interesting than the vanilla fighter. They easily bully the fighter into a corner and steal his lunch money without breaking a sweat. Also, they way the maneuvers work allows some flexibility to use them outside of combat as well.
If you want a more specialized approach, there are several classes that are better than the fighter in some specific area (especially skills or utility) but not as general and adaptable (e.g. often you're pretty much set on your fighting style). You have:
Further, there is the "Thug" class variant from UA that trades some weapon and armor proficiencies and the level 1 bonus feat for a much better skill list and more skill points.