So I've seen a lot of variants of builds like this and I made an evil NPC for a game I'm running play as one. I'm thinking about maybe playing 1 in a campaign that I'm about to play in but, I'm not sure. There are 2 things that the character relies on heavily, the knowledge skills (specifically Arcana, Dungeoneering, Local, Nature, Religion, and the Planes) and the Knowledge Devotion Feat (you make a Knowledge check based on creature type to gain a bonus on attack and damage rolls). There's 5 ways to make Knowledge skills better or more easily accessable that I know of.
1st: Able Learner, all skills cost 1 skill point but, cross class skills can still only have half as many skill points and you can only be a Human, Doppelganger, or if your DM isn't super strict a Changeling (my DM's not super strict).
2nd: Changeling Rogue variant from Races of Ebberon, instead of getting trapsense you gain a +1 on all Knowledge checks when you would gain trapsense but, your still not trained in the Knowledge skill.
3rd: Dragonfire Adepts can get an Invocation called Draconic Knowledge which gives them a +6 on all Knowledge (and Spellcraft) checks for 24 hours and they're treated as being trained in those skills while this is active.
4th: Lunatic Insight, this is a Feat from Heroes of Horror that requires you to have a mild depravity (if you don't know what a depravity is it's a downside you get from being tainted but, you can qualify for some feats because of it). You are treated as being trained in all Knowledge skills plus you get a +2 on initiative and on saves against mind-affecting spells and abilities.
5th: Factotum, is trained in all class skills and has quite a few intelligence bonuses.
Right now I'm still debating on what race to play. All books are open and some dragon (it depends on whether or not one of the players or DM has the issue or can find it somewhere). Right now I'm debating between a Changeling (to go into the Rogue variant), a Gray Elf (for the +2 dex, +2 int, I'm not too conserned with my str and con because I'm hoping to not get hit a lot), and a Nezumi (+2 dex and 40ft. base speed) we haven't rolled our stats so I have no idea what they'll be other than that none of them will be under 10 (that's just how we roll, sorry I saw an opportunity for a corny pun and had to).
We're starting at 3rd level (flaws are allowed) so right off I'm thinking Swashbuckler 3 (for Int to damage) with my feats like this: Weapon Finesse (Swashbuckler bonus), Lunatic Insight (1st, already talked this over with my DM and he ok'd it), Knowledge Devotion (Flaw 1), Combat Expertise (Flaw 2), Exotic Weapon Proficiency: Broad Blade Short Sword (3rd, the weapons from Complete Adventurer if I take a -2 on attack rolls with Combat Expertise I gain an additional +1 AC)
From here I'm not sure where to go, Rogue for sneak attack? Scout for better speed and skirmish? Two Weapon Fighting/Improved Buckler Defense (for a +4 from combat expertise and using 2 BB Short Swords and the bonus from a buckler)? A level of Dragonfire Adept (which I don't think would really fit) for +6 on all knowledge checks? Warblade for more intelligence stuff? Factotum and just say screw it to Lunatic Insight and possibly even swashbuckler (as nice as some of the Factotum abilities are I don't really like the idea of the Factotum class), I'm really not sure. All help is appreciated.
I've found the Draconic Knowledge feat to be invaluable for this kind of thing.
Human Dragonfire Adept 1 (next two levels are yours to decide)
Remember, Dragonfire Adept gives you Dragontouched as a bonus feat at 1st level, so you count as a Sorcerer of your character level for taking draconic feats.
Feats taken: Draconic Heritage (1HD), Draconic Knowledge (Human), Draconic Senses (flaw).
Now you use the Draconic Knowledge invocation. You have a +9 bonus pre-Intelligence, pre-ranks on all knowledge checks (which are also forever more class skills for you) plus a +4 bonus on Spot, Search, and Listen in addition to the low-light vision and Darkvision 60ft. On average, this is +2 attack & damage against any foe.
Using a second flaw, you can swap Human out for a different race of your choice. You can also multiclass away from Dragonfire Adept without fear: you got what you want out of it. Just be sure to grab Draconic feats when available as each one you pick up gives you a +1 bonus on all knowledge checks, on spot/listen/search checks, and on saving throws vs. sleep and paralysis. Your fourth Draconic Feat also gives you Blindsense 20ft.
If your DM rules that the Dragonfire Adept invocations count as arcane spells, Draconic Vigor would be a good one so you can self-heal outside of combat.
EDIT: This route also means you don't need to worry about the crap that is taint if you're alive.
The Vile feat Insane Defiance (from Exemplars of Evil or that other evil book that was the last 3.5 one printed) is really nice for typical "weak willed" fighter types. It lets you redirect a Mind Affecting spell to someone else.
Don't get me wrong a +9 on all my Knowledge checks before my intelligence bonus and anything else is great but, I'm not to familiar with the idea. Also I'm only trained in the knowledge skills while the invocation is active, I'm not sure if my DM would let me put ranks in the Knowledge skills in that case (even though the invocation is active for 24 hours). Do you know if Draconic Invocations can be dispelled? I haven't really looked into the class that much.
Invocations can be dispelled, but you can use it at-will so you just replace it if it does. Also, you can always put ranks into a skill unless you have hit your cap. You haven't (you still have 0 ranks), so you can invest those skill points in Knowledge.
Just want to mention two more options concerning knowledge:
* Duskblade has int-based casting, full bab, and access to knowledge skills.
* Dwarves have access to Ancestral Knowledge feat (RoS) that makes knowledges depend on wisdom. Works well e.g. with cloistered cleric. Not exactly int-based though 
A Truenamer can actually make for an interesting defensive fighter, and has all knowledge skills as class skills. Intelligence is his base stat, so it synergizes with the knowlege checks.
There is a recitation that allows you to take a total defensive action, and gives you a bonus to your AC equal to 1/3 your truenamer level. Combine this with quickened utterances, and you can still "cast" every turn, and be an AC monkey.
Combine this with Combat Expertise, a Defending weapon, a shield or that metal sleeve thing from the arms and equipment guide, and some nice armor and you are a decent ac fighter. Also get insightful reflexes and a ring of evasion and you are good to go.
Ok, I guess I should explain my character goal a little better (because looking back on it I didn't do a very good job at that). Apperently in the world the DM made magic is being outlawed (which is why I wasn't to into Factotum or Dragonfire Adept). I'm still debating between 2 wep. fighting or relying on one sword and Knowledge Devotion. I'm trying to get my AC pretty high, it doesn't have to be godly but, with con being one of my dump stats I need to not get hit that much. I would also like to somehow obtain a godly speed/initiative which is why I was thinking of the Nezumi race and the Scout Class. I was thinking about going into Blade Dancer but, it has to be able to cast arcane or divine spells and we're not allowed to use the oriental adventures books.
In games we've played in the past we've allowed people playing Swordsages to take the Kung Fu Genious Feat so their Wis based abilities worked with Int instead, then if they took Monk levels it would apply to that as well. I was thinking about possibly taking 2 Swordsage levels so I could have Int to AC and wear armor. Does anyone know of another class that can do this? I don't mind the Swordsage or it's abilities but, I'm trying to stay away from ToB now because I found out 2 of the other party members are an Unarmed Swordsage (going for Shadow Sun Ninja, don't ask why this is allowed but, Oriental Adventures isn't it's beyond me) and a Crusader.
Sorry for all this extra stuff. O! Also about the taint thing. My DM said all I have to do is pick 1 depravity and I have it without any other effects so I'm thinking for roleplaying purposes the Hysterical depravity. Sure I can only take a move or standard action the second round but, it'll fit the character nicely.