I have to put my vote out for:
Magician by Raymond Feist
(And of course all the subsiquent books, but they would take too long to list)
The Dragonbone Chair, Stone of Farewell, and To Green Angel Tower (aka the memory, sorrow, and thorn trilogy) by Tad Williams
and of course... Any and all Discworld books! by the one and only Terry Pratchet. You don't nessisarily want to start with the first books, as they arn't as much fun as some of the later ones. I especially liked Reaper Man.
I could be rattling off all the names of good fantasy writers, and the works I have liked of theirs, but that would take too long, and these are ones that I really liked, that I can see on a shelf near me
Oh but a word of caution... Get a forklift if you want to read Memory, Sorrow, and Thorn in hardback, and prepair to hurt your hand holding the paperbacks
... pretty darn big books.