If you like the complex world building of Martin, then allow me to recommend the Chronicles of Thomas Covenant by Stephen R. Donaldson.
Really good books (there will be a total of 10, with 9 published so far and the 10th due out next year, and unlike Martin, Donaldson is very serious about his writing, you can count on the fact that he will actually finish the series [in fact, he updated his blog last December saying the 10th book was in rough draft form, he just has to do the rewrites and he's done]).
His style is a bit hard sometimes, like Tolkien. He likes to use big words, so it's no easy read like Salvatore or Rowling. But it is well worth the effort involved. The story he tells is pretty amazing. In fact I like all of his stuff, he's done some Sci-Fi as well that is very good.
Also, I like Stephen King's Dark Tower series as well, so another recommendation for that one.