Mistral! I'm shocked! How could you not suggest Space Viking
(doesn't get more opera than this) and Cosmic Computer aka Junkyard Planet
? Both by Piper. Space Viking has even seen a reprint in the last few years, picked up a new copy a couple months ago.
The Berserker books by Fred Saberhagen (and now other authors)
Still waiting for someone to write a Berserker VS Bolo book. That would rock!