The rash of zombie threads was my sole reason for joining the forums - I'm ashamed to admit the number of times I've watched some of my favorites. I had a class in college where we got to watch several vampire movies (best credits I ever earned) and some of the ones that have become favorites:
1) The Hunger (The Bowie.)
2) The Lost Boys (I have not watched the sequel yet, I'm a little afraid.)
3) Bram Stoker's Dracula -- I know, I know, this one was kind of awful, but something about young-goth-Gary-Oldman does it for me. A completely useless Carey Elwes also provided major entertainment value (and I say this as someone who worships The Princess Bride...and Saw).
4) OK, I admit it, I love From Dusk 'Til Dawn.

Anything that has Tom Savini introducing himself as "Sex Machine" is an automatic win.
Khell, I have a soft spot for Once Bitten, too...something about the geeky virginal Jim Carrey gets me every time!
Loved the first Underworld, fell asleep during the 2nd, and couldn't get into 30 Days of Night (I loved the premise but something in the execution didn't sit right with me).