The Bridge at Remagen. The Big Red One. Ice Cold In Alex.
Battle of Britain. Dambusters. Tora! Tora! Tora! Midway.
The Cruel Sea. Sink The Bismark.
These are considered very accurate films (aside from some small changes for marketability or storytelling):
The Great Escape (some yanks added for marketing purposes)
Battleground (especially for its time)
12 O'Clock High
Best Years of Our Lives (about US vets returning home)
Cockleshell Heroes
The Man With No Name
Das Boot
Pearl Harbor (ok, J/K)
Kelly's Heroes is known for decent accuracy in its use of tactics and weaponry (except the Tiger since none then existed for use) and is a very entertaining movie.
Non- WWII:
Gettysburg
Zulu
All Quiet on the Western Front