Great answers, all. I'm a little weird, and like "How Green Was My Valley" Don't ask why, I can't tell you. Casablanca is right up there, along with The African Queen, too.
On gun movies, with due deference to Split Second ("Bigger Guns! We need bigger guns!"), All Quiet, Bridge Too Far, Bridge over Kwai, Apocalypse Now, Dog Day Afternoon, Ocean's Eleven, Zulu ("It's a miracle, all right. A .45 Boxer Henry miracle."), The Blue Max, Boondock Saints, and the other fine movies already mentioned, I've got to go with Red River. Although, Sink The Bismarck has some really nice guns in it........
Besides the movies we've all seen a thousand times, I also recommend a host of foreign war movies. Talvisota/The Winter War, Stalingrad, Das Boot, and Burnt By The Sun all spring to mind.
Steve