I'll reprint here a post I made in a thread a couple of months ago. It was one of my first posts, and it failed to revive the thread. (Perhaps better luck here?):
I have these books:
1. Bettas: A Complete Introduction by Walt Maurus
2. Bettas by Marshall E. Ostrow
3. Your Happy Healthy Pet: Betta(2nd Edition) by John H. Tullock
4. Quick and Easy Betta Care by T.F.H. Publications
5. Bettas: A Complete Pet Owner's Manual by Robert J. Goldstein, Ph.D.
6. Siamese Fighting Fish: Care, Selection, Breeding by Gene A. Lucas, Ph.D.
7. The Betta Handbook by Robert J. Goldstein, Ph.D.
8. Animal Planet Aquarium Care of Bettas by David E. Boruchowitz
9. Caring for Betta Fish: An Insider's Guide for Betta Lovers by Marcus Song
I especially like the Animal Planet book, Goldstein's Bettas: A Complete Pet Owner's Manual, Quick and Easy Betta Care and Song's book, which costs around $26; perhaps it can be had for less. A few of these I have not read yet. Several came through Amazon Marketplace, and the Lucas book came from IBC.