Char Aznable (CCA)
The Red Comet...need I say more. Despite rumors about his sexual preferences he is still the original villian of gundam and his evil actions fit the series well. He pilots some of the soolest mechs, drops an asteroid on earth, and despite being owned by Amuro in the end he mocks him unitl their mutual sparkly doom.
Iron Mask (F91)
There was sooo much more potential for this guy and the entire F91 storyline. It was supposed ot be a 50 episode series after all. But the mask still has one of my favorite lines of all time "This is a family matter." It still send sshivers down my spine when he says it.

Norris Packard (8th MS)
Owns an entire MS battalion and goes down like the badass that he his. Awesomeness embodied in a blue moblie suite and a chubby guy....who say that comming?

Rau Le Creuset (GS)
Rau is one of my all time favorite villians and has the best "I'm so bad and there's nothing you can do about it moment" when he totally owns everyone that comes near him at the end of Gundam seed. I also enjoy his little speech to Mu and Kira in the genetics lab, so creepy. (shiver)
Paptimus Scirocco (MSZ)
Ahh dear Master Paptimus. He creates some of my favorite mechs and completly takesover the Titans with a single bullet. A villian to the bitter end I loved that he turned Camille into a vegtable as his last living act...he gave that angsty teen a cheerly outlook on life in the end. It was a vast improvement.

Well those are my top favs, your turn now. Sorry if their is already a board like this, but I can't find it so blah on them.