1. JRR Tolkien
The phenomenon. Of all the books I've read, regardless of genre, the Silmarillion remains my absolute favorite. I also love the history of middle-earth books which deal with the Sil. The LoTR is also in my top 5 but has by now been slightly surpassed by a few other works. Incredible trilogy, but nothing beats the grand spectacle of the First Age, with the Elves in their magnificent splendour and the world relatively unspoiled, facing the great power of He Who Arises in Might (anyone who can think of such a telling name deserves praise).
2. GRR Martin
One hell of a writer, epic Fantasy at it's best, he does have one or two things I'm not that crazy about but he does a great job with characterization and worldbuilding. He manages to handle multiple storylines better than anyone I've seen, and his previous books hint at great and very exotic things to come.
3. R. Hobb
Only just below Martin. Her characterization also is supreme, with Fitz coming in as my all-time favorite fiction character. She doesn't beat Martin because his is a more ambitious tale, while hers is more intimate. I love both, but I think Liveship is nothing special, therefore if I have to choose, she goes to three. But again, wonderful characters combined with a world so enchanting that I'd actually want to live there. Also one of the most tragic romances that I've ever encountered.
4. Marcus Herniman
Unknown author published in the UK but not in the US. Writer of a stunning Fantasy trilogy in a pseudo-medieval world (my favorite sort) with lots of interesting magical human creatures, the best portrayel of the Fay that I've ever seen outside of the master himself, Gods with powers that have actual influence in the real world, a terrifying and beatiful enemy, a world populated with wonderful cities based on our world's renaissance period, truly vast forests inhabited by enigmatic beings, an elaborate magic system and a foulplaying emperor.
Much of it may sound repetitive but I enjoyed it much more than so many of the so-called original Fantasy books. I think anyone who enjoyed Tolkien would like him. Note: he has a character appendix which is larger than even Eriksons
5. A tie between two vastly different authors, Steven Erikson and Guy Gavriel Kay. Both superstars in their own right and hardly inferior to any of the authors mentioned above.