I was gonna make this a poll, but there are too many choices to just clump into an "other" category.

Here are some films that come to mind...

-Saving Private Ryan
-Platoon
-Full Metal Jacket
-The Bridge on the River Kwai
-Enemy At The Gates
-Black Hawk Down
-Three Kings
-Born on the Fourth of July
-We Were Soldiers
-The Thin Red Line
-Tora! Tora! Tora!
-Patton
-Apocalypse Now
-A Bridge Too Far
-The Longest Day


I'd go with Saving Private Ryan, followed by Full Metal Jacket.