Ah, where to start?
Tolkien is great, obviously. The world building is incredible (I taught myself to read and write elvish, heh), and I especially like the literary aspect to it. Most modern fantasy seems to be written for children, and as such the quality of the writing in most of it is awful. As an English professor, Tolkien took his writing seriously.
Garth Nix and Phillip Pullman are two that haven't been mentioned before. Their books are aimed at a younger audience, but it's still good fantasy.
After, Tolkien, my favorite is probably Ursula le Guin - surprisingly, another who hasn't been mentioned. Her Earthsea cycle is phenomenal, and most of her other books (some are sci-fi) are well worth reading too. Another somewhat similar writer is Patricia McKillip (the Riddle of Stars trilogy was incredible, but I haven't read much else by her).
Oh, and Jacqueline Carey. She hasn't written much, but I've thoroughly enjoyed what books of hers I've been able to find.
Anyways, I tried to stick to mentioning authors that nobody's brought up yet (well, besides Tolkien), just to get something new in here. Has anyone else read these?
And one last thing. I've used the list at
Best Fantasy Books to find some really neat fantasy on occasion, though there's also a lot on the list I don't agree with. Anyone else seen the site?