Best movie plot twist?!

Best movie plot twist?

What's the movie with the best plot twist you've ever seen? That moment where every thing turned in a new direction that took you totally by surprise. (Just don't give away the plot twist in case someone hasn't seen your film yet)

6 days ago
I had four favorites in mind and I was curious to see if they would appear in anyone else's answers - three of them did: The Sixth Sense, The Crying Game, and The Usual Suspects. The fourth one is a great old B&W movie that has a lot of humor and another great surprise ending - Witness for the Prosecution. Definitely worth taking a look at. Thanks to everyone who came up with suggestions I haven't seen yet.

Planet of the Apes. The 1968 version with Charlton Heston.