The best one we've played is Tour of Darkness for Savage Worlds (SW). The game is set in the Viet Nam war, which made it very accessible for my players having relatives who fought in the war and having seen all the movies we grew up watching. They really got into the story. Fewer fantastic elements might have been better, but it was fun. One player recently dubbed it the standard by which all other such games should be judged.
It is from their Weird Wars series, and Weird Ward II has now been released for SW. I think SW would make a fine military game with just the core book. The Explorer's Edition is only $10, so it is very affordable.