Akito Sohma (Fruits Basket) -So psycho it's beautiful.
Shinobu Sensui (Yu Yu Hakusho) -I hate the guy, but he's an excellent villain.
Seishirou Sakurazuka (Tokyo Babylon/X) -Even knowing how horrible he is, it's so hard to hate him.
Kharl (Dragon Knights) -Crazy = awesome.
Saabel (Dragon Knights) -He's so pathetic, it's adorable.
A lot of the villains from the last season of Sailor Moon, particularly Sailor Lethe.
Hisoka (Hunter x Hunter) - Creepy + Crazy = All Around Win
Emperor Kura (Planet Ladder) -...He was just awesome.
Favorite at the moment:
Dark Ashura (RG Veda) -
Prima Donna of Destruction Er...no comment.