Animal House (who knew he'd become a Senator?
Beat me to "The Machinist." Wasn't a very good movie in my opinion, but the twist was cool.
Not a big Nicholas Cage fan at all, but the twist in Matchstick Men was its saving grace for me.
There's always classics like Psycho and Citizen Kane that I suppose had a twist ending (*Spoiler Warning* It was his SLED!)
Saw's twist ending fooled me too; mostly because the movie affectively suspended my disbelief for the first 90% of it.
My roommate loved Vanilla Sky for it's twist ending; I thought it was mediocre at best.
I've also heard Mulholland Drive, although its twist was obscured by its excessive weirdness (still worth a look) and Donnie Darko, which is a bit culty.
My modern favorites are "Suspects" and "Fight Club" probably.
If you're a battery, you're either working or you're dead....