So far I can't help but notice the distinct absence of Terry Goodkind's 12-book Sword of Truth series, and Robert Jordan (and Brandon Sanderson)'s 15-book Wheel of Time series. No love for these major, best-selling, generation-crossing fantasies?
Wizard's First Rule (the first book in the Sword of Truth series) is without question the worst book I have ever read. Just jaw-droppingly awful.
Series that are rather less awful, in no particular order:
C.J. Cherryh's Fortress and Morgaine books.
Steven Brust's Vlad Taltos books (and spin-offs).
Jim Butcher's Dresden Files (his Codex Aliera is readable but ultimately pointless).
Garth Nix's Old Kindom Trilogy (
Sabriel,
Lirael,
Abhorsen).
F. Paul Wilson's Repairman Jack series.
Jack Vance's Dying Earth and Lyonesse books.
Gene Wolfe's
Book of the New Sun (if you view it as fantasy rather than s.f.).
Pratchett's Discworld.
Glen Cook's Black Company. His Garrett, P.I. books are also fun.
Michael Moorcock's Elric, Hawkmoon, and Corum books.
Guy Gavriel Kay's work post-Fionavar, particularly
Tigana.
Lois McMaster Bujold's Chalion books.
Fritz Leiber's Fafhrd and the Gray Mouser books.