Can't go wrong with the Kubrick and Hitchcock bodies of work.
Another good movie I recently saw was
The Searchers. I had heard a lot about this movie, how it was John Wayne's favourite role, and how it influenced a number of major films for decades following its release, including Star Wars. In fact, when you watch The Searchers you can see that it blazed the trail for several notorious movie scenes.
It is an epic movie, set throughout the Western USA over a span of 5 or 6 years. As a 50's era western, it does have some slow parts, and the action sequences lack the punch and realism that we are now accustomed to. But it is an impressive and influential film, and it's story and characters have haunted me since I saw it.
http://www.imdb.com/find?s=all&q=the+searchers