I just finished reading these three books, one after the other:
- Starship Troopers (don't confuse the unsubtle movie with the classic book)
- The Forever War
- Old Man's War
In basic outline, each book has exactly the same plot, about a man joining the army in some future war. Each have many of the classic war-story elements, including the tough over-the-top drill Sargent in basic training.
At the same time, all three are totally different, in different universes with different physics and different politics and enemies. And, perhaps most importantly, each with a different outlook on war and its necessity. Each one is awesome individually but created an amazing accidental trilogy when read together.