This list includes many of the books and series that inspired the Game of Tomes, but it cannot be exhaustive, since so many minds go into creating this:
A Song of Ice and Fire by George R.R. Martin (of course!)
Watership Down by Richard Adams
Wind in the Willows by Kenneth Grahame
The Cthulhu Mythos by H.P. Lovecraft (and others)
Redwall by Brian Jacques
The Last Herald-Mage of Valdemar series by Mercedes Lackey
Lord of the Rings series by J.R.R. Tolkien
Diskworld series by Sir Terry Pratchett
World of Darkness RPGs
A variety of military sci-fi and military fantasy series (The Vorkosigan Saga, Honor Harrington novels, works by Eric Flint, Harry Turtledove, etc.)
Fairytales and folklore from around the world
Memes. All the memes. (Does this belong in this category or the next one?)