+1 for Chigurh.
The Coen brothers and Cormac McCarthy are made for each other, as both have a good line in villains. My favourite examples are J. E. Freeman as The Dane in the Coen’s Miller’s Crossing and The Judge from McCarthy’s Blood Meridian.
Other favourites:
Snoop, from The Wire (arguably, she wasn’t even acting).
Todd from Breaking Bad – A moral vacuum who acts and speaks like an unusually polite 12-year-old.
Stephen Rae as Gatehouse from The Shadow Line – like a more evil George Smiley. Rafe Spall as Jay Wratten in the same show provided a very nice contrast: unhinged, capricious and, again, oddly child-like. Reminded me of another favourite: Miranda Richardson as Queenie from Blackadder!