Personally, I’d say you’re about done with fighter and swashbuckler
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.
Classes
The best answer is warblade (but you don’t have that allowed)
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.
You already have Int to damage: factotum adds Int to (almost) everything else
(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 already qualify for chameleon, and it’s pretty good
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).
If you qualify for that, you might also make a good master of masks
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.
Dread commando is fitting, but not very strong
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.
A little bit of bard could work
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 is OK for a few levels
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.
If you can, refluff a barbarian
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.
Marshals are OK if you’ve got great Charisma
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 leaders certainly fit the bill—if your DM is using the Commander rules
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.
Feats
Daring Outlaw would improve your damage
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.
Daring Warrior isn’t too good
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.
Knowledge Devotion is pretty solid
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.
Conclusion
A bunch of dips for useful abilities
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 simple option: Daring Outlaw and dread commando
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.
I really do have to mention warblade again
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.
For basics, Beguiler 1/Wizard 4/Ultimate Magus 10 (or however far you get) is by-far the best choice. Beguiler 2/Wizard 3 as entry is not going to get you killed or anything, but it is a dramatic loss of power relative to only a single lost wizard level.
Cloaked Casting
From an optimization perspective, Cloaked Casting isn’t nearly worth what you lose in terms of wizard spellcasting.
Unfortunately, Cloaked Casting is rather minor in general. There’s no reason you can’t surprise your opponents with your spells, and just not get the +1 DC bonus. Surprising people is usually a pretty good idea anyway (though feinting in combat is not). You will be better off doing things this way.
But feel free if you really want Cloaked Casting to get it. Just be aware that it will cost you more than it ought to.
You don’t have to ban Illusion if you don’t want to
Wizards get illusions that beguilers don’t, and your wizard spellcasting will be superior to your beguiler spellcasting. If illusions are important to you, keep it on your wizard; having it on both classes will really play up its importance to your character.
So illusion could be very valuable to you; don’t ban it just because you think it will be redundant. It won’t be if you use it right.
You really don’t need area-damage
Conjuration and illusion are excellent at battlefield control, which means rather than simply damaging people in areas, you’re hitting people in areas with nastier effects, and stuff that warriors cannot do. Damage is easy, and lots of classes do it as well, if not better, than spellcasters. In a lot of cases, though, that’s all they can do. So let them do it.
And ban evocation.
Metamagic
Go for it! Ultimate magus gives you powerful abilities that allow you to use your second class to power metamagic for the first, which works very well. Definitely a good choice.
Shadow Spells
Ideally, you do not want to use shadow evocation or shadow conjuration offensively, because you give the enemy two chances to save, which is bad. As such, I don’t really suggest relying on them for that; they’re massively better as buffs or what have you. Spell Focus (Illusion) is still a solid idea though.
Best Answer
Warmage: Just a bad class
The warmage spell list is pretty awful, and Warmage Edge just doesn’t add enough damage to be worth it.1 Armored spellcasting is much too easy to do to get excited by it as a class feature.
Finally, note that warmage class features frequently don’t help wizard spells:
and
Neither of them is worth much in general, but they’re worth much less to you.
Long and short: adding wizard to a warmage certainly helps the warmage, but it doesn’t help the wizard much.
1 In fact, Warmage Edge isn’t even worth investing in Intelligence for a single-classed warmage above, say, level 5; the damage just isn’t enough to justify diverting resources from Charisma, Constitution, and Dexterity. At very low levels, it can be a kind of significant amount of damage, possibly justifying some investment.
Sorcerer: Far more powerful, broken with dragonwrought shenanigans
Sorcerer gets a far better spell list than the warmage, and with Greater Draconic Rite of Passage, you can make up one of your missed levels. With Loredrake (which you arguably might qualify for but a DM would have to be insane to let you), you can make up a lot more.
Ultimately, I recommend sorcerer, but not the shenanigans. They aren’t necessary and just break the game.
Beguiler: Not mentioned, worth considering
The enchantment/illusion version of the warmage, but without a lot of the problems. Like the warmage, the beguiler comes with a more-or-less static list of spells, but knows all of them. Unlike the warmage, that list is quite good, and moreover beguiler spellcasting is based on Intelligence, which works quite nicely for a wizard. Finally, it’s a 6+Int skill class, so it makes a great choice for ECL 1 when you get ×4. Just throwing it out there. Ultimately, you can probably do more with the sorcerer because the sor/wiz list is so great, plus there’s always dragonwrought shenanigans uniquely available for sorcerer, but beguiler is in many ways easier (less diving for spells) and more elegant (all Int-based).