There's loads of these here:
http://www.reddit.com/r/reddit.com/c...s_its_a_movie/
These are good too: if you watch Pretty Woman backwards, it's about a rich woman whose boyfriend makes her become a prostitute. If you watch Goonies backwards it's about children leaving a perfectly good pirate ship to chase an Italian family through a scary maze.
I love the Jaws one though.