Greatest Villain!

[Mark]

Saruman

 

[Kai Lord]

George Lucas.

 

[DerianCypher]

I'm not sure that he exactly qualifies as hero or villain but Q from star trek

DC

 

[Tonguez]

Come on everyone loves Darth Vader!
(even if Anakin is a whiney dork)

Second choice Thulsa Doom

and yeah Q counts

 

[Hand of Evil]

Loki
Satan
Darth Vader
Stormbringer
Nazis

 

[jdavis]

Yosimite Sam

 

[KenM]

Mordan from Babylon 5.

 

[Nightfall]

Apocalypse
Sauron
Morgoth
The Dark One from WoT
Lord Foul
Chryine by Micheal Stackpole

 

[Severion]

Archibald Cunningham from Rob Roy

and i second George Lucas

 

[Chun-tzu]

The Fox network, for tanking just about every good series they've ever picked up.

Darth Vader, for sheer presence.
David Xanatos (Gargoyles), for sheer Machiavellian badness.