1. Dwight Schrute, the Office. I think we could argue whether or not Dwight is an antagonist; after all, the show doesn't really have a clearly defined protagonist. I think Jim is the closest thing to a protagonist, so Dwight would be a clear antagonist in that case.
I think Jim is the closest thing to a protagonist, but in that case I also I like Michael as the antagonist. However, I like him a little to much to think of him as "the bad guy" he's more just the well-meaning idiot who tries a little too hard. Or way too hard. Same thing with Dwight. But that's why that show is great...there are no clearly defined roles. And really Jim and Pam are total jerks to Dwight most of the time! (Except in that one episode when Dwight had just gotten dumped by Angela and he was competing against the computer and beat it and Pam saw how sad he was so she IM'd as the computer that he was the superior being. That was so nice!)
Okay wasnt gonna do a list but here's one anyway:
5. Roman - Big Love
4. Scorpius - Farscape
3. The Monarch - The Venture Bros
2. Weyoun - Star Trek: Deep Space 9
1. Gul Dukat - Star Trek: Deep Space 9
And just for fun, my favourite antagonists turned protagonists - Garek and Damar, both from DS9. I kind of love Cardassians...and the Dominion. Yeah I'm a nerd, and what?