The Berserker series by Fred Saberhagen.
The John Grimes Rim World series by A. Bertram Chandler.
The Stainless Steel Rat series by Harry Harrison.
The Gentle Giants series by James Hogan.
The Ringworld series by Larry Niven.
Other singles:
Rendezvous with Rama, by Arthur C. Clarke.
-PJ
You may like the Bolo series by Keith Laumer.