TLoR thread gave me this idea. My favorites would have to be:
Uller Uprising, Space Pirates, Lord Kalvan, and Lone Star Planet by H. Beam Piper
West of Honor by Jerry Pournelle
Retief and Bolo novels by Keith Lamaur
Soldier Ask Not, Dorsai, and Wolfling by Gordon R. Dickson
The Unpleasant Profession of Jonathan Hoag, Glory Road, Job: A Comedy of Justice, and all the Lazarus Long books by Robert A. Heinlein
Star Rangers by Andre Norton
The Hammer's Slammers and General series by David Drake
Footfall by Pournelle and Larry Niven
The Chtorr series by David Gerrold
The Beserker series by Fred Saberhagen
Passage at Arms by Glen Cook
Starhammer by Christopher Rowley (a real sleeper hit)
The Dune series by Frank Herbert. The prequels by his son are good too.
...well, as you can see, I haven't met many sci-fi books I didn't like
So, what are yours?