Elves, in all their variations. Because of their elegance, and their affinity for chaos. Also, you can usually find a subrace that fits a certain class (ok, most of them have -2 Con, which hurts, but you can't just have strengths).
Beyond that, fey'ri (which are demonic tiefling elves) and full-fledged succubi/incubi are a world of fun.
All these choices lend themselves well to my favourite concept: The rogue - which can take the form of the actual rogue class, or of generally skilled and sneaky classes. ATM, I play a gestalt incubus (his monster HD make up one of the two classes) / soulknive, who will become an elocater soon (for the soulknive part) and either become rogue to continue after succubus is done, or advance in soulknive (or both).
I like characters with high Dex, Int and Cha, who can be sneaky and useful aout of combat, too.