I think I really like the villains who are driven by a sense of moral code or social obligation. Most villains are just purely malicious and power/greed hungry. But I like the ones that really believe that what they're doing is for a good cause. Like Magneto, or Dexter. There may be other examples.
Either Castor Trow, from face/off, or Cyrus Grissom, from Con Air.
Lee Van Cleef in The Good the Bad and the Ugly. He was the baddest of the bad.
Sauron from lord of the rings! Not that stupid pterodactyl that can sort of hypnotize people from the X men or whatever he's from!
That's not a question I'm ever going to be able to give a definite answer to, but I'll go with Pinhead this time.
I demand a recount!
Megamind cause he has a Killer sound track