I just want to point out that a large percentage of actors from Joss Whedon's television show 'Firefly' feature as villains in other shows. Five of the nine central characters are adversaries in other Whedon shows (more than half - that's a lot), and one more is a baddie in a new science fiction show (2/3).
Nathan Fillion, the hilarious and rebellious Captain Mal Reynolds on 'Firefly.'
On 'Buffy the Vampire Slayer' as as Caleb, a misogynistic former priest and serial killer (I never actually saw him on this).
And extra points as the reprehensibly arrogant Captain Hammer, both the antagonist and "hero" of 'Dr. Horrible's Sing-Along Blog.'
Gina Torres on 'Firefly' as the badass Zoe Washburne.
On 'Angel' as the creepily serene and lovey-dovey goddess Jasmine.
Adam Baldwin plays the ignorant, amoral, and extraordinarily macho Jayne Cobb on 'Firefly.'
Still large, but much more polished as the sinister 'Angel' character Marcus Hamilton.
Morena Baccarin is 'Firefly's' classy courtesan Inara Serra.
So far I haven't seen anything too drastic on the new scifi show 'V' (though I have only seen parts of it, so I don't know for sure), but the alien Anna's eerie smile hides plans for world domination.
Summer Glau is 'Firefly's' River Tam, resident brilliant crazy and a potential weapon of mass destruction.
She plays Bennett Halverson, another genius, far more terrifying, psychotic, and sadistic, on Whedon's 'Dollhouse.' (There was a very appropriate picture with the signs "danger" and "caution" behind her.)
And finally, (SPOILER, I guess, even though it's not much of one anymore) Alan Tudyk's 'Firefly' persona is the wise-cracking, vaguely insecure hotshot pilot Wash.
Still funny, but about 1,000x crazier and more violent, Tudyk plays Alpha, a once-wanna-be serial killer who is imprinted with about 40 different entire personalities (not split personalities, though one of them is). This grants him serial killer status, since he now has mad brain power and reflexes. Probably one of the best villains ever. Plus, I guess Tudyk was bad on V along with Baccarin.
I just find this Firefly=evil stuff funny. And cool.