Here's a few fun ones:
Exoticist is a Fighter variant from Dragon 310. You trade proficiency in all martial weapons for 4 exotic weapons. Additionally, one of your bonus feats can be Exotic Attack, which is just a +2 bonus on trip attempts with an exotic weapon (and +2 Disarm). Very useful for Spiked Chain tripper builds.
Corsair is another Fighter variant from the same book. You lose proficiencies in heavier armors and your skill lists get juggled about, but you gain a few rather silly abilities for free at level 1 and 2. Only one is really worth considering... the ability to swing on a rope and then bull rush someone, gaining a +1 bonus on the bull rush for every 5' swung. Could be hilarious, if situational, for Dungencrashers. You also get the ability to grapple people using swim checks if you're in deep water, which has some interesting potential.
There's also the Fencer variant, which is a heavily Charisma based Fighter. You have to take 4 levels in it to get the one interesting ability, which lets you make opposed Charisma checks with an enemy as a standard action. If you win, they take a -2 BAB penalty (yes, that's base attack bonus, which can lower their attacks), with an additional -1 penalty per 5 points you win by. If you can somehow pump the heck out of your Charisma, this could be very cool... I'm thinking some sort of wacky Arcane Duelist or Iaijutsu Master build.
And finally the one other people have heard of... the Targetteer. You give up martial melee weapon proficiency for two exotic ranged weapons, and get special bonus feats available to you like "use dex to damage with ranged attacks against enemies vulnerable to crits" and "get two extra ranged attacks but all attacks get -5 to hit."
Arcane Disciple is actually a Cleric variant that gets any Sorcerer/Wizard or Bard spell as a divine spell at each level. It loses Turn Undead, but their existence could be wonderful for Archivists.