For me the best will always be
Heath Ledger as THE JOKER : The Dark Knight
Perfect portrayal of a psychopath, memorables quotes and mimicks, enjoyed it so much
The Motherfucker in Kick Ass 2 play by Christopher Mintz-Plasse was pretty entertaining too, not the best performance ever but a good done.
Yuri Boyka from Undisputed 2 play by Scott Adkins. The character got such a cult following he had his own movie for part 3 and part 4 is on the way still starring him
Thomas Gabriel from Live Free or Die Hard play by Timothy Olyphant , lot of people hate on that movie but i loved it, Bruce Willis was as good as always, and Gabriel had presence
Jean Vilain from Expendables 2 played by Jean-Claude Van Damme. He truly had fun with the role, wish there would had been more, loved it
Agent Smith from Matrix , iconic, good presence
and finally...
Clyde Shelton played by Gerard Butler in Law Abiding Citizen, i just love the character and rooted for him all movie long... never did i liked a vilain that much as an original one(Ledger was awesome but its an iconic character he played)
Of course i let out the slasher movies characters like Freddy Kruger or Chucky, altough the vilains thecnically they are the attraction of the movie ...
Oh and on TV...
Crowley in Supernatural is one of the rare vilain i like to follow, even tough he is never always completely a vilain, despite being ... well KING OF HELL lol, he is one of the driving force of the show since a couple seasons.
Also i always loved Spike from Buffy the Vampire slayer as a vilain, even tough he was clearly a vilain for only 1 season more or less, before occiling back and fourth until becoming a good guy. That show had great vilains, sometimes better than there heroes counterparts, The Mayor in season 3, Faith when she turned bad, its my guilty pleasure,a show of my teen/early adulthood years, but still