Zulu starring Michael Caine would have to be my favourite. The sight of 4000 authentic Zulu extras chanting war cries before charging Rorke's Drift is one of the most emotional scenes in film, especially when the Welsh reply with 'Men of Harlech".
I liked
Saving Private Ryan, and
Starship Troopers.
Black Hawk Down and
We Were Soldiers were ok, a little... American I guess.
Another good one to catch is
300 Spartans. The combat is a bit tacky, and the special effects barely deserving of the name, but the last stand of the Spartans again is a stirring moment.
Oh, and I can't forget
Braveheart, even if the shocking historical inaccuaracies grate.