Well I've seen a shitload.
In no specific order..
WW1
The Lost Battallion (2001)
Sergeant York
WW2
American Guerillas in the Phillipenes
The Longest Day
1941
The Guns of Navarone
Force 10 from Navarone
Raid on Rommel
Patton
A Bridge Too Far
The Bridge at Ramagen
Castle Keep
The Dirty Dozen
Battle of the Bulge
Stalag 17
The Great Escape
Battle of Britain
Memphis Belle
Band of Brothers
Saving Private Ryan
Sands of Iwo Jima
The Thin Red Line
U-571
Da Boot (omfg best submarine movie ever)
Run Silent Run Deep (w0rd up Clark Gable)
Kelly's Heroes
Tora! Tora! Tora!
Pearl Harbor (sucked ASS)
Operation Petticoat
Vietnam
Apocalypes Now
Forest Gump (kind of counts)
Platoon
Flight of the Intruder
Missing in Action 1, 2, 3
Full Metal Jacket
The Green Berets (Only movie about Vietnam made during the war)
I have also seen countless films from these genres + the korean war, that I can't recall at the moment.