My own personal favourites...
Gary Oldman as Norman Stansfield in Leon
Bobby D as Max Cady in Cape Fear
The inimitable Cristoph Waltz as Colonel Hans Landa in Inglorious Bastards
A very underrated (ever so polite and camp as a row of tents) bad guy imo - Taylor Negron as Milo in the Last Boy Scout
And a real old school baddass; Lee Van Cleef - Angel Eyes in TGTBATU
Honourable mentions for Hans Gruber - Die Hard, Clarence Boddicker - Robocop, Frank - Once Upon a Time In The West, Vincent Coccotti - True Romance, Alonzo Harris - Training Day, Simon Phoenix - Demolition Man, Agent Smith - The Matrix, Commissaire Sauveur Cristini - Doberman