I am looking for some good mystery movies. What do you think is the best Whodunnit?

Seven and The Usual Suspects spring immediately to mind

AND THEN THERE WERE NONE
WITNESS FOR THE PROSECUTION

Mmmm lemme see... The Usual suspects, Angel Heart , any Agatha Christie and Hitchcock movie, The Game maybe?

Kiss The Girls

yeah. definitely go with the usual suspects

The Usual Suspects

Other than whats been mentioned I like L.A. Confidential

And for a fun whodunit Clue.

Clue is a good choice, because if you select the option to watch it with the random ending, you can ask yourself "whodunit?" even when you watch it again.

Clue
Gosford Park
Scream

I would not class Usual Suspects as a Who-dun-it. Who-dun-its are murder mysteries based on facts, not one where the last 10 seconds erase the entire movie.

Classics would be AND THEN THERE WERE NONE, any Sherlock Holmes film (more cerebal) MURDER BY DEATH (spoof)any Agatha Christie film (the best being MURDER ON THE ORIENT EXPRESS), the Poriot series, Lord Winfrey, the old Paul Temple British shows (hard to track down, well worth it), the new Nero Wolfe show on A&E, and there are plenty more.

CLUE is a spoof, as are most later hollywood ones. I would stay away from Gosford Park, it's more of a political picture than anything else. Very dissapointing.

Dead Again had a cool ending. I didn't see that one coming.

If you like "Whodunnits" I also suggest the television series "Monk."

Murder by Death - mystery combined with off-beat comedy.