Foucault's Pendulum (Umberto Eco)
Excellent, excellent book. Not an easy read though.
I've read a lot of non-fantasy and scifi, but as far as these genres are concerned:
When I was younger:
Moorcock's Elric and Corum series'
Leiber's Fafhrd and Grey Mouser series
Eddings' Belgariad
Tolkein's Hobbit and LotR
Asimov's Foundation series
C.S. Lewis' Chronicles of Narnia
Then later:
CS Friedman's Coldfire trilogy
Various Gaiman books (not graphic novels)
GRR Martin's Song of Ice and fire series
John C. Wright's Orphan's of Chaos (starting on this one now)
China Mieville's New Crobuzon books.
Lots of others, I just can't remember them all. I am sure I am leaving out some good ones too.