Ah, a forum topic I feel capable of adding to....
Some have obviously been mentioned, and in no particular order:
McAffrey - Pern series (first few anyway)
Heinlein - Starship Troopers plus others
David Gemmell - Drenai & Sipstrassi series particularly
David Eddings - Belgariad & Mallorean series
Weis and Hickman - Dragonlance chronicles, the Twins trilogy, Death Gate cycle
Stephenson (probably my favourite author) - Baroque Cycle for "Historical Fantasy" plus Snow Crash and Cryptonomicon
Donaldson - Thomas Covenant
Asimov - Foundation series (first 3 or so)
Iain M. Banks - culture series and others
Peter F Hamilton
Herbert - Dune
Fritz Leiber - fully agree with earlier post, a severly under-rated contributor to the genre
these I didn't see earlier:
Guy Gavriel Kay - Tigana, Song for Arbonne, Lions of Al-Rassan, Fionavar Tapestry Trilogy, Sarantine Mosaic (2 books). Kay bases a lot of his books on obvious historical facts (Al-Rassan is Moorish Spain, Sarantine is c6th century Byzantium) but has an almost unbelievable emotional depth to his writing.
Alastair Reynolds - kind of similar to Hamilton's "Space Opera" style
Scott Lynch - the Gentleman Bastards books - possibly the most original modern fantasy I've come across - "Fantasy Hustle" (for BBC viewers).
China Mieville - very good short stories
Daniel Keyes - Flowers for Algernon
Mmm, have to leave it there, it's tricky thinking while the Manchester Derby is also on.....
