Doctor Doom, lord of Latveria. What's not to love about this guy? He's got the looks, the schemes, the powers, and most importantly, the presentation. The hammiest villain is the best villain in my book.
Magneto, master of magnetism. I love this villain because he isn't really a villain -- rather, an extremist who wants to make sure no one of his kind has to experience what he has been through.
Thanos, the carrier of the Infinity Gauntlet. All you really need to know about this guy is that he's literally in love with Death, and wants to court her... by extinguishing all life in the universe. Yeah. Needless to say, he's quite a menacing villain.