Speaking of Baldur's Gate, I'm gonna go with Sarveok from the orig. Baldur's Gate game. He freaked me out from the opening cut when you first launch the game O_o And the last battle with him is freaky and down right awesome.

I remember Planescape: Torment, great ending and though the boss wouldn't be on my favorite villians list the ending to that game would be in my top five favorite endings list.

Lots of sephiroths....cool...

I always thought Mecha-Hitler from Wolfenstein 3D was awesome. I mean come on, it's Hitler for cryin' out loud.

Kefka!

dr. wily

Baby bowser. :D