That Harry Potter thread prompted me to revive this thread. What are your favorite science-fiction and fantasy novels and why?
Warning: this post reflects my personal opinions and tastes only.
I've read the standard fantasy fare when I was younger, Tolkien, Zelazny (Amber), Le Guin (Earthsea), Ann McCaffrey (Pern), Moorcock (Elric of Melnibone, Dorian Hawkmoon), even some of the Weis and Hickman AD&D stuff, which I think is really awful.
These days however, I really can't stand the standard high fantasy stuff, though in moments of weakness that embarass me, I sometimes still feel compelled to buy Robert Jordan's "Wheel of Time" stuff.
I haven't read many science-fiction novels, though that's what I'm mostly interested in these days in fiction. I'm more of a fan of the short story format. I recommend Asimov magazine to such fans.
One author I really would like to plug is Australian Greg Egan. His stuff just blows me away through the sheer richness of his imagination. This is real hard science-fiction though and not for the faint of heart. Egan's stuff is neither plot driven nor character driven. It's purely idea driven and for me this epitomizes the best of what SF means.
http://gregegan.customer.netspace.net.au/