I see people have mentioned the following:
The Usual Suspects
Donnie Darko
both pretty similar really. the plot twist comes at the very end of the film, & enRAB the film. Usual plot twist in a film is a lot earlier, & is needed to explain what happened, as most of it wont have made any sense. In Usual Suspects & Donnie Darko, what happens before the twist does make sense.
Elephant
its a reaction art film, purely a reaction to a real event. its basically saying 'look at whats happened'. its not meant to be analysed to death, if your doing that, youve got it all wrong.