You'll find plenty of books in Madness&Magic. I think it's a nice way to add flavor to the world you've created without beating the player over the head with all the lore. The books are there and the player can choose to check them out if he wants to.
Some of the books are about the universe the module is set in.
Some are about the history of the dimensions you'll visit.
Then there is fiction...
And of course, silly books - my favorites.