I haven't found anything too similar to the Game of Thrones series, but after looking online for similar reading...I came across a series called the Wheel of Time. 14 books in the collection, similar grandeur of plot and setting to Game of Thrones, and it's kept me entertained through the 6th book so far.
If you haven't already, give The Lord of the Rings series a read, starting with the hobbit. Like usual, much better than the movies...although the movies followed these books more closely than most do.