Second that, but I'd also vote for Thulsa Doom from the Kull books.

SHODAN from System Shock 2 -> Unmatched evil AI performance
Arthas as Dark Knight in Warcraft 3 -> Awfully boring and pretentious human daddy's boy becomes an extremely cool and ruthless undead leader
T-Bag from Prison Break -> Intelligent and resourceful villain who deep down just wanted to be a good guy but it was not meant to be

I like Baron Zemo from the MCU. He has no powers but still managed to win. The xenos and the predators from the movies are also cool villains. They're not really bad guys but are doing what they are doing because of instinct and their culture.

Not a villain per se, but the Markers/Brethren Moons from Dead Space. Simply because of how unusual it was, it got stuck in my head for some reason.

that is probably among one of the greatest videos I've ever watched. and even when he's trying not to be he's still funny.

My favorites:

1. Skeletor
2. Baron Harkonnen
3. Obi Wan
4. Gary Oldman

He is if your a Sith.

well i mean the sith kinda wanted to be left alone but the jedi are just as evil

It's hard to choose between The Borg from Star Trek TNG, HAL 9000 from 2001: A Space Odyssey, A.M. from I Have No Mouth, and I Must scream, Kira from Death Note, Gustavo Fring from Breaking Bad, Amy Elliott Dunne from Gone Girl, John Doe from Seven, Hannibal Lecter from The Silence of the Lambs, or The Society from Martyrs.

After seeing this recently declassified secret footage from inside the White House I now believe that Ronald Reagan was the great's evil genius who ever lived and not the senile old man we all though he was.

https://www.youtube.com/watch?v=b5wfPlgKFh8

So many cool villains and I am only familiar with half of them.
Imho most villains are more memorable than the heroes.

Nice :P

Continuing Breja's theme of Ricardo Montalban: Vincent Ludvig (the naked gun) - " How could you do something so vicious?

Vincent Ludwig : It was easy my dear. You forget, I spent two years as a building contractor. "

Also, Reboot's Megabyte (voiced by Tony Jay) - https://www.youtube.com/watch?v=-D8Yde_rqgU&t=20m45s

Megabyte from Reboot that takes me back, watching that whole show you see him moving from a children's TV villain in early episodes to full on crazed dictator in later ordering his men into suicidal bloodbaths just to make a point.