Top 10 villians of all time!

[Jack Lupino]

From movies, games, comics, manga, etc

1  Aizen (Bleach)
2  Greed (Full Metal Alchemist)
3  Sigma (Megaman X)
4  Boris (Golden Eye)
5  The Terminator
6  Mr Blonde (Perfect Dark)
7  Hans Gruber (Die Hard)
8  Vinnie Cognitti (Max Payne)
9  Frieza (Dragon Ball Z)
10 Megabyte (Reboot)

well, it might not be in completely correct order but it should be right up there.
post your own, discuss, rant, rage etc

[WilllemNL]

1. Bowser (mario)
2. Arcturus Mengsk (starcraft)
3. Kain (red alert)
4. Sauron (lorf of the rings)

Dunno about the rest. 

[gaijin]

1. The Borg.

[dezo]

[evilcandybag]

1. The Borg.

Fixed =)

My own list:
Darth Sidious (Star Wars)
Anti-Spirals (Gurren Lagann)
The Demiurge (Kult PnPRPG)
Kefka (FFVI)
Victor von Doom, aka Dr Doom (Marvel Comics)
Ganon (Zelda)
Kane (C & C)
Walter o'Dim/The Man in Black/Randall Flagg (several Stephen King novels)
Gollum (LotR)

I'm not going to number them, since I don't know which one I prefer. I will, however, motivate my choices.
Doom, Ganon, Kane and Walter are all tenacious villains. Once defeated, they come back, again and again. Defeat is always "just a minor setback" on their way to total world domination/godhood or whatever. Doom makes it into this category not by being immortal or timeless like the other three, but by sheer willpower and stubbornness, which is a great merit in itself.
The anti-spirals and the demiurge make the list together for doing something so grand as to remove a whole race from godhood (or god-like status) to "protect the universe". Both have constructed extremely elaborate systems to keep mankind in place, and elaborate systems are part of what makes a good villain.
Kefka is an evil, insane clown who aspires to godhood and succeeds in grasping it and reshapes the world as he sees fit. You don't get more villainous than that.
Sidious makes the list for being a brilliant schemer, twisting an entire galaxy to his will. That and being the best in the world at saying "Goooooood".
Gollum makes it here for being the most complex villain in the LotR books as well as the world's most awesome junkie.

Comments on other's lists:
I don't think Sauron (post Silmarillion) is a very interesting villain. As he appears in the LotR trilogy, he's almost not even a proper character, but much more like a backdrop to create other villains from.
I don't really see the Borg as villains, really (I deny the existence of the Borg Queen, she's just silly). They are more like a force of nature, akin to the Nothing in the Neverending Story.

[Crazywater]

Bad Horse. The Goombas. The RIAA. George W. Bush. Bill Gates. Rick Astley. Also, that guy who invented getting up early.

Edit: Oh, and that pirate from Rayman 2.

[WilllemNL]

Ooh yeah, Darth Sidious, that's a nice one. I like Darth Traya too. That little bitch really pursuaded me to live life the way she sees it, she REALLY convinced me in that Star Wars game that Jedi and Sith are both silly and you should see the Force as the Force and nothing more...
...and then she fucking betrays me and appears as a Sith. Fucking hell! I could kill her! Well, I did!

@evilcandybag: You read the silmarillion? I did twice, and I've forgotten about 90% of it again I think. I view Sauron as quite a legendary villain, he fucked up the world pretty much before the books/movie. Perhaps I should pick Morgoth then...

[Harvey Danger]

Boris from GoldenEye? Really? He sucked in the movie AND the game.

[Torp v2.0]

The Demiurge (Kult PnPRPG)

Fancy seeing that guy pop up on your list...

[evilcandybag]

The Demiurge (Kult PnPRPG)

Fancy seeing that guy pop up on your list...

I've read the Kult 3rd edition rulebook more times than I've read LotR and Shogun toghether.

[Sirix]

in no particular order.

1. Light (Death Note)
2. Lavos (Chrono Trigger)
3. Dancin' (Mystical Ninja: Starring Goemon)
4. Kefka (FFVI)
5. Envy (Full Metal Alchemist) [Rad, I'm surprised you chose Greed for your FMA villain. He was cool, but more of a nuissance in comparison to some of the other homunculi, like Envy. He's the biggest asshole around]
6. Yggdrasil (Tales of Symphonia)
7. Colonel Hans Landa - The Jew Hunter (Inglorious Basterds)
8. Bill (Kill Bill)
9. Big Brother (1984)
10. Agent Smith (The Matrix)

wow, it was harder to come up with 10 than I thought.

[Jack Lupino]

I chose Greed because he's just fucking cool =)

[WilllemNL]

Oooh, Light from Death Note. That one's epic too.

And Ozzymandias from Watchmen, the way he is portayed in the comic is incredible. One of the few characters who's been completely changed in the movie. Where he says he'd catch a bullet, the look on his face.. 
And his plan / scheme is just pure evil. To do good. He does evil.

[Smeagol]

1. Mecha Hitler - Wolfenstein 3d

Reality as subtext. Dictator as a robot with miniguns as text text.

2. President of the US - Fallout 2

"Yeah so the Vaults were a sadistic experiment with no real tangible goal in sight, we just felt like being dicks. Also, these guys right over here? We're gonna experiment on them reeeeeeeeeal good now if that's okay with you."

3. Wolfram and Hart - Angel series 1-5

If they were just normal lawyers, they'd probably be higher. The fact that they openly work mostly for evil demons/utterly repugnant people actually makes them look good compared to their generic kin.

4. The Daleks - Doctor Who

Think Mecha Hitler as above and you're pretty close. Lower down due to recent badass decay.

5. Marlo Stanfield - The Wire

One quote really; "It's the other way"

6. Gabriel 'Sylar' Grey - Heroes

Hey there psychopathic guy with huge eyebrows who is immortal and has a fetish for slicing people's head open telepathically then examining the exposed brains which somehow let you collect all kinds of ridiculously cool superpowers! Pity you keep getting stopped by those meddling kids* though.
_{* Everyone in the entire series who's still alive at the end of each arc. At the end of every single arc without fail. Go team original writing!}

7. Rossum Corp - Dollhouse

Utterly repellent mind-wiping organisation who whore out their brainwashed drones to those willing to pay. This is them playing nice.

8. Warden Norton - The Shawshank Redemption

"You, banking guy. Help me embezzle hundreds of thousands of dollars and I'll make prison life for you more bearable. No? Fine, spend 3 months locked in a hole that's roughly the size of you, with no light or contact with anyone."

9. The Megacorps - Syndicate

"Gentlemen, life in a suburban shithole is unbearable, this is a fact. The solution? No, not social improvement, we have a more profitable approach. Why not take a powerful hallucinogen that keeps you doped up all the time and unaware of the squalor you live in?"

"Why don't we have it render the population incredibly susceptible to our marketing boys at the same time it induces this drug-fuelled bliss? I mean, if we're helping cure everyone of their misery, we may as well remove their free-will at the same time and force them to buy more of our shit."

"You genius."

10. Angelus - Buffy the Vampire Slayer/Angel

Good lord, Angelus. What's worse than a vampire competent enough to survive for over 500 years? Oh yeah, one who happens to love torturing people until they become gibbering insane wrecks. Then turning those gibbering insane wrecks into immortal blood-sucking killing machines. Dracula, eat your overly dramatic heart out.

More entries for TV shows then anything else as the villains actually have time to be characterised properly. Also, no I did not forget about Schindler's List entirely. Mecha Hitler is on there as he's only extrapolated from a real character, as opposed to being a real person, which sort of seems to defeat the point of this sort of thing.

[Jack Lupino]

Awesome list!