Anyway... I voted for Orcus, Vecna and Strahd. Orcus because he's the classic demon prince, Vecna because he's the Lord of Secrets and has a great backstory, and Strahd for sheer classy lethality. I am disappointed by the lack of Eberron support, though, because both Vol and the Lord of Blades are great villains.
Although technically not a D&D villian (unless you've got the first printing of Deities & Demigods, 1e) I'd have to say Cthulhu and Hastur rank up there as classic villains as well. Hastur in particular is pretty nifty; the whole you can't say his name three times without him nabbing you was a D&Dism, as a matter of fact. In fact, Hastur
I voted for Sammaster because he's supposedly the guy who invented the process of making a Dracolich and then managed to convince some pretty powerful people to start worshipping undead dragons for generations to come.
My first choice would have been Graz'zt, but he wasn't there. If anybody remembers the Planes of Chaos boxed set from Planescape, they should take a look at Graz'zt again. He held onto three layers of the Abyss (something no one else has done AFAIK) and his ambitions include sucking an entire Crystal Sphere into the Abyss to be a fourth layer under his dominion.