1) Excluding the ones you've already mentioned (Darth Vader would top any list of villains), here are my top 5. I'm thinking these should not just be one-dimensional 'baddies' like Biff Tannen or Henchman #2, but characters that should be feared as much for their brains as their brawn. Too deep?

1 - Alan Rickman as Hans Gruber in Die Hard
2 - Robert Mitchum (and Robert DeNiro) as Max Cady in Cape Fear
3 - Kevin Spacey in Seven
4 - Gary Oldman as the dirty cop in Leon: The Professional
5 - Kathy Bates as Annie Wilkes in Misery

Honorable mention - Billy Zane in Dead Calm

2) Mel Gibson - Payback

He was a Bad Guy that played the Good Bad Guy.....

I dont know... does that count???

3) Dr. Claw from Inspector Gadget

4) Christopher Walken in At Close Range

Joe Pesci in Goodfellas

Alan Clark in Snatch

5) I'm with Biker Ben. Dr. Claw creeped me out. I'll also add the Shredder from TMNT to the list.

6) Cillian Murphy (had to look his name up!) as Dr. Crane in Batman Begins.

James Anderson as Bob Ewell in To Kill a Mockingbird

Dennis Franz (Lt. Norman Buntz) in Hillstreet Blues (I still can't watch the guy in anything--he just makes me mad to see him)

Michael Des Barres (Murdoc) - MacGyver (the guy could NOT be killed!)

Richardo Montalban (KHAANNN!) - Star Trek

7) Bill Lumbergh, Peter's boss in Office Space.

8) Alan Rickman - good call. As the Sheriff of Nottingham and Professor Snape too!

9) Lumbergh - Good one!

Dr. Claw was very creepy...now the theme song is in my head.

Lets see:
Danny Glover - Color Purple
Oscar the Grouch - Sesame Street
Gargamel - Smurfs

10) Unfair, Lumbergh was just doing his job under difficult circumstances. If anything, the villain is the manager of Chachkees or whatever that place is called.

11) I'm thinkin' the Reverend Henry Kane freaked me out in Poltergeist II - The Other Side. Oh, and Jack Palance was always good.

12) So many great villains here. My first thought, of course, was Vader, with Palpatine right behind. But then I thought of Russ's Number 4 above: Gary Oldman in The Professional.

A note for those who don't know about the Chotchkie's Manager mentioned by LimeyGeorge - that's the director, Mike Judge.

13) The character Benjamin Linus in the TV show Lost. That guy is creeeeeepy! I love to hate him, though.

14) Ahh....soundchick....good one! I wasn't thinking TV shows....and I'm not (100%) convinced yet that Ben is evil, but he totally fits the criteria as far as creep factor goes.

15) Paul Bettany was scary in The DaVinci Code as Silas, the albino monk.

16) LimeyGeorge, anyone who asks someone to come to work on a Saturday is a villain in my book.

17) #1 Darth Vader, hands down.
But I definitely have to say, Kaiser Soze-Usual Suspects. One of the best twists and greatest villans in the movie to date.

18) Moobi, I thought you would list Scorpius from "Farscape."

19) So many options and directions to go here. Most of the good ones I could come up with have been said. Vader tops my list at Numero Uno. Kaizer Soze is great too. How about the bay guy from Boondock Saints who ended up being their father? Could Willem Dafoe could be considered the bad guy from Boondock Saints too? He was great in that flick. Also, I would have to throw a vote out there for the principal from Ferris Bueller's Day Off. (As you can tell I did not research these actual names of the actors or persons they played.)

That gives me 3 (4 if you include Willem Dafoe). Places 4 and 5 would have to go to the aliens that killed Optimus Prime in the Transformers Movie. This was not Megatron but the two aliens that were able to actually killed Optimus Prime. Anyone know what I am talking about here?

Last but not least I would say Joaquin Phoenix in Gladiator. I would love to carve out his heart with a spoon in that movie. I think I have never hated a bad guy more than I hated him in my entire life.

Those are my top 5 (6 if you want to be strict) bad guys of all time.

20) Niki, I agree with you on that work/Saturday villian thing! :)

21) Bill, I can't believe I didn't think of Scorpius either. Frell!

For Walker:
The principal from Ferris Bueller was Ed Rooney played by Jeffrey Jones. That's a movie Bill and I have watched more times than I can remember. I never watched Transformers: The Movie all the way through, so I don't know which Decepticons killed Prime, although I would bet dollars to donuts one of them was Starscream. And I think the name of the Emperor Phoenix played was Octavius. Won't swear on it, though.

22) The Usual Suspects is one of my favorites and Kaiser Soze is definately a great villain once you realize who he is. My other choices would be Michael Madsen as Mr. Blonde from Reservoir Dogs cutting off the guys ear and Francis from Pee Wee's Big Adventure.

23) Francis. Didn't see that one coming.

24) I just thought of another good one. The Warden in The Shawshank Redemption.

25) Arvin Sloan from Alias has to make my top 5.

26) Joe Pesci in Casino, Al Pacino in Scarface, and of course James Gandolfini as Tony Soprano.

27) Oh, speaking of prisons, the guy in O'Brother, Where Art Thou? who stalked the escaped prisons and nearly hanged them.

Or the guard in Cool Hand Luke ... or was it the warden of the camp?

28) Ah, I forgot about the warden from Shawshank. Good call. He certainly was a bad man and a great acting performance as well.