Peregrinator wrote:The Forever War by Joe Haldeman
Ender's Game by Orson Scott Card
All of the Falkenberg's Legion yarns by Jerry Pournelle, including the books he wrote with S.M. Stirling. Top it off by reading The Mote in God's Eye by Niven and Pournelle which might not be categorized as pure military SF but is something that everyone should read (it takes place in the same universe as Falkenberg's Legion).
The Man-Kzin Wars series.
For something new, Marko Kloos' Frontlines series.
There's at least one sequel to Mote in God's Eye (which IS a masterpiece). I think it is called The Gripping Hand. And I believe there may be a story or two out there.
By the way, this has the most interesting group of aliens I have ever come across.