In no particular order...
"Funboy" from The Crow
"Darth Vader" from The Empire Strikes Back
(as evil as he was in A New Hope, he was just the vilest in this one...
"Randall Flagg" in Stephen King's The Stand
That Flesh Pirate leader guy (with the crazy eyes) in Cyborg
"Agent Smith" in The Matrix Trilogy
"Roy Batty" in Blade Runner
"Darkness" in Legend
"Kurgan" in Highlander
"Captain Rhodes" in George A. Romero's Day of the Dead
"Tim Rothman" in charge of X-Men