Jerry Pournelle's Falkenberg series (part of the Co-Dominium setting)
- West of Honor
- Mercenary
- Prince of Mercenaries
- Go Tell the Spartans and Prince of Sparta
All fairly realistic decent tales of near-future military exploits. The first three are about a mercenary unit - interestingly written before the 1990s rise of private security firms.
Set in the same universe:
- King David's Spaceship - An adventuring party goes to another planet to recover knowledge of how to build their own space ship.
- The Mote in God's Eye - An excellent tale of first encounter with another species.
Uncle Ted