J.R.R Tolkien Everything (up to publication of Silmarillion)
Edgar Rice Burroughs John Carter of Mars, Tarzan
Robert E. Howard Conan
Fritz Leiber Fafred and Grey Mouser
Fred Saberhagen Empire of the East, The Books of Swords
Harvard Lampoon Bored of the Rings
Douglas Adams Hitchhikers' Guide to the Galaxy
Various Thieves' World
Michael Moorcock Elric Saga, Chronicles of Corum
H.P. Lovecraft Everything
George R. R. Martin Song of Ice and Fire series
Jack Vance Lyonesse Trilogy
Gene Wolf Book of the New Sun, The Knight
Brian Aldiss Halyconia Trilogy
I read The Lord of the Rings over and over and over again when I was a kid. I'd estimate that there's easily 6 cover-to-cover-to-cover-to-cover-to-cover-to-cover reads before I was 15. Then there were the times I felt like re-reading Moria, Bombadil, Helm's Deep, Fangorn, etc etc etc.
Saberhagen's Empire of the East (collected trilogy of novels) and then his Books of Swords (even the early Lost Swords) - which I read just after finishing the first Shanarra trilogy, thank ye gads! - really blew my mind. I was able to decouple from an absolutely Tolkien-centric universe.
Enter the Multiverse! The Crawling Chaos! Etc. Then I really stopped reading fantasy for a long time. All of the books mentioned had a bearing on my game-play - though many histories, philosophies, and other non-fictions (Machiavelli, Loren Eisley, John McPhee) here go unmentioned. And a boatload of sci-fi and other fictions (Murakami, Borges, Margaret Atwood, Stanislaw Lem, Phillip K. Dick, Bester, Bear, Benford, Brin, Brunner, Niven & Pournelle, etc etc etc)
I don't remember who tipped me off to Game of Thrones, but I do remember that it was late summer of 2003. It was the first thing that I'd read in years that really just made me want to play RPGs.
Other readings had inspired some writing, brain-storming development sessions, but as I continued that series, I just kept getting more and more steam up to play a damn game. So I went to the FLGS (Collectables, Etc.) and played some 3rd. Didn't 'do it' for me, but whatever.
Since then, Aldiss and Gene Wolf and Mr. Vance have each had a huge impact.