Honorable Mention: John Lithgow as Lord John Whorfin/Dr. Emilio Lizardo in The Adventures of Buckaroo Banzai Across the Eighth Dimension.

Honorable Mention: Marlon Brando as Dr. Moreau in The Island of Dr. Moreau. (Hey, Moreau is an awesome mad doctor... Too bad this movie sucked.)

And the top 5:
5. Vincent Price as Dr. Phibes in The Abominable Dr. Phibes. Kiss me baby.

4. SkekTek the Skeksis (voiced by puppeteer Steve Whitmire) in The Dark Crystal. Scared the essence out of me as a kid. Still does.

3. Jeffery Combs as Dr. Herbert West in Re-Animator. Get that damn needle away from me.

3. Maximillian Schell as Dr. Hans Reinhardt in The Black Hole. Killer robots, zombie crew, and a bitchin' God complex.

1. Colin Clive as Dr. Henry Frankenstein in Frankenstein. Yes, It's Alive!

So who did I miss?