The Postman Always Rings Twice by James M. Cain

What a fantastic read!  It reads somewhat like a traditional crime novel, but it has such a sophisticated twist, that it is really something more.  Frank, a drifter, becomes involved with Cora, a married woman, and the two conspire to kill Nick, her husband.  It is really short and a very fast read, so it's ideal for most situations.  Easily worth the time.