I thought about dear ol' Vader earlier in the thread, but for some reason didn't post it. Lecter's certainly a classic one, too.

Here's a fun one to add to the mix - HAL 9000. It may be somewhat debatable if he quite qualifies as a villian (certainly falls into Sanjay's category of well-intentioned, as his acts were the result a need to deal with conflicting instructions rather than malice) and he doesn't necessarily fit as "the ultimate" bad guy, but the acts themselves and the challenge that his behavior represented are unique.

"What do you think you're doing, Dave?..."

How about ol' SATAN in The Exorcist. Or the shark in Jaws. Both of those movies were so above the standard for scary that years later when they were finally shown on commercial TV they had disclaimers about being unsuitable for small children.
I had to go back to the theater to see The Exorcist on my own because my girlfriend couldn't stay past the 360 neck turn. People actually got physically ill when they saw it the first time. When you think about some of the stuff in todays movies these movies seem tame.

Don't forget the little beastie in "Alien" too. People screamed out loud when that thing burst out the first time.

Jack Palance just looked evil and mean in any movie he played in.

Richard Boone in " Big Jake".

The two above were born to be bad.They look as menacing in person as on the screen.

On that note, Al Lettier really fit the tough guy / bad guy mold. He played opposite Steve McQueen in "The Getaway" and Virgil "The Turk" Sollozo in "The Godfather."

He was one mean looking mofo'.

I recall a few people on the forum (myself included) talking about the Brazilian movie City Of God. I'd say that the gangster character Little Zé qualifies as ruthless.

There's been a lot of good ones, but I think I'll list a few:

No Country For old men ( I think this was a fantastic movie)
Se7en
The Bone Collector
American Psycho

oh and don't forget Silence of the Lamb series with our dear friend Dr. Hannidbal Lecter. That was a tasty series.

My favorite Villain is hands down Keyser Söze/ Verbal Kint Played by Kevin Spacey in The Usual Suspects.

A close second would go to The Joker by Heath Ledger in The Dark Night.

How about Mr. Brown in Reservoir Dogs?

That is a good one had not even thought of Mr Brown