We have a thread about overrated so let's do one about underrated. I start :
-Before sunrise , to me is a masterpiece and not many people know about it. Also great European scenery:
http://www.imdb.com/title/tt0112471/
-Joyeux Noel. This french movie is based on a true story, that happened in 1914. during the First World War. There was a Christmas truce, the war continued the next day. I think it's a great movie, sad too.
http://www.imdb.com/title/tt0424205/
-Sphere, it is a great movie about a spaceship, that not many people know.
Can't think more by now...post yours.