I would say Tyki from D.gray-man. He is so HOT!!!

Itachi from Naruto definitely. <3

I can't really think of anybody right now... But at the top of my head...

Atobe Keigo from The Prince of Tennis. I have fights with my friends at this day and age if he's gay or not, but he's MINE!!!
Feast your eyes upon his sexy evil-ness:

Atobe prince tennis images, Atobe prince tennis pictures, and Atobe prince tennis photos on Photobucket

Yura of the Hair from Inuyasha:

Urds mom in AMG :> the arch devil/demon

Sephiroth from Final Fantasy VII. He may be crazy as f*ck, but hey I'd do him.

sephiroth, hes bloody HOT, and Aoshi shinomori and seta sojirou from rurouni kenshin^^

Sephiroth is pretty fucking hot. I think I can speak for every FF7 fan when I say we've all thought about being in bed with him/being him.

But really. It's obvious isn't it? The sexiest anime villain is Queen Beryl.

Everyone's suggestions, upset for Kish, for I am not pedo bear! :o
BB from Los Angeles BB murder cases, Another Note PLZ?!???!

I like me some L, and the shinigami eyes boost his sexy level.

I think it would be Freya (aka Dark Chii) [Chobits].:D