Well, I like setting books.
Spellbound, The Ruins of Myth Drannor, City of Splendors, Menzoberranzan, Ruins of Zhentil Keep, Empires of the Shining Sea, Ruins of Undermountain, The North Guide to The Savage Frontier, The Ruins of Myth Drannor.
Also, flavor books are very interesting.
Complete Elves, Complete Rogue, The Seven Sisters, Volo's Guide's, Cult of the Dragon.
To name a few
but I don't know what you have so I thought I'd give eough examples to work with.
