(yeah, I was a sci-fi geek. deal with it.)
Me too! I have read hundreds and hundreds of SF books, I would have to say in no particular order that these authors pretty much never disappoint -
Heinlein up to and including 'Stranger in a Strange Land,' pretty spotty after that.
Poul Anderson
Neal Stephenson
John Boyd - may have to stay with it a bit to get fully engaged with the story but once you do, wow!
Norman Spinrad - a true master of his craft
Andre Norton for younger readers (But some of them, like
Time Traders, are great at any age)
Larry Niven, including the collaborations with Pournelle (Some of the extended Ringworld cycle stories get a bit to in-bred)
Jack Vance - Some of the shorter stuff obviously written to pay the bills but still good. Very wry humor.
John Brunner - Also wrote a lot of short bill-payers, but some true classics as well.
Keith Laumer - Who doesn't like Retief and Bolos?
Eric Frank Russell
C. M. Kornbluth and the Pohl/Kornbluth collaborations - "The Marching Morons" is a must-read
H. Beam Piper
Harry Turtledove - Not so much the semi-fantasy, which is unexceptional; his alternate history series are good but milked out much too far
Gordon R. Dickson
S.M. Stirling - occasionally overdoes the bad-assery, and painted himself into a corner that way in the silly-premised Draka series
David Drake - Fantastic military SF, unexceptional fantasy
Ahh, I could go on, but that's more than anyone here will recognize anyway...