George R. R. Martin has already gotten a few remarks. His "Song of Ice and Fire" is incredible. It is a huge story that is supposed to last 6 books or so. I think 3 is out and another is in the making( has been a long wait though )
Robin Hobb's books has the same depth and atmosphere as Martins books but they are not quite so brutal...well ..then again
They should be read in this sequence:
The Farseer Trilogy
The Liveship Traders
The Tawny Man
Robert Holdstock, a british fantasy writer, wrote a series of books that really broke the fantasy mold. "Mythago Wood" and "Lavondyss" may demand quite a bit of the reader, but they are both extremely rewarding. "Lavondyss" has one of the most memorable female characters imo.
Lynn Flewelling's Tamir Series deals with gender in a very original way..and talking about memorable characters; Brother is a wonder..
Sci Fi:
Never liked the Thomas Covenant books...The Gap Series i loved. There is one helluva rollercoaster ride in those books.
Ian Watson, The Embedding, The Jonah Kit, and almost any other book by him will blow your mind.
oh BTW..i think China Mieville is severely overrated. Not Dan Brown overrated though