I'll be adding to this list as I locate more books that I think are worth owning. You can order these titles direct from Amazon.com. I've had nothing but excellent service from them so let me know if you experience otherwise.
This was the first book I found that had any definitive information on Hymenochirus. The photos throughout the book are the highest quality I've seen anywhere. A good general amphibian reference.
This title comes highly recommended as a valuable reference source for aquarists regardless of the species being kept. Good information on setting up and maintaining a tank.