If you haven't delved into George RR Martin, I highly recommend him. The Game of Thrones series (ASOIAF) is getting some well deserved attention because of the HBO series, but I'd recommend his older works such as The Armageddon Rag, Fevere Dream, and his short fiction such as the collection A Song For Lya as well. He's just a great writer.
Another author that I cannot recommend highly enough is David Morrell. The Fifth Profession and the trilogy The Brotherhood of the Rose, The Fraternity of the Stone, and The League of Night and Fog are standounts, but you won't go far wrong with anything he's written. His short story Orange is for Anguish, Blue for Insanity is one of the best horror shorts ever written, IMO.
And if you want to get caught up in a good (long) series of books set in an imaginary world, you could do a lot worse than the Necroscope series from Brian Lumley. Really great stuff.