My favorite is probably Full Metal Jacket or Das Boot.
Isn't Das Boot generally considered the greatest war movie ever made?
According to film critics, such as Roger Ebert, the greatest war movie ever made is Apocalypse Now, because it shows the darker sides of human nature:
Das Boot is considered to be a quite mediocre film in artistic terms and it is not anywhere near the greatest war movies and not even among the greatest WW2 movies. I found it entertaining but nothing really special.
I think that the greatest WW2 movie ever made would be Grave of the Fireflies, which is actually an anime movie, but it has been said by some to be the film which generates the strongest emotional reaction ever made. The whole film is available on youtube.
Here is Ebert's coments on it:
[ame=http://www.youtube.com/watch?v=_9WEyuMq0Yk]Film critic Roger Ebert - Grave of The Fireflies - YouTube[/ame]