One Flew Over the Cuckoo's Nest
Director: Milos Forman
Jack Nicholson gives a fantastic performance as an offbeat, unconventional convict who makes a show of being psychologically disturbed in order to be sent to a "nuthouse" and escape spending his time in jail. The movie is a frighteningly dark look at how we are defined within society, and how society exerts itself to keep those definitions in place to preserve its systemic norms.
The movie doesn't condense well (read: too complicated for me to be bothered at this moment) but as themes go, those are pretty hefty. I haven't read the book, but it's one of those that I "should" read - and after watching this movie, I'm dying to.