If you only want to check out one gardening book, I would recommend A Garden Book for Houston and the Gulf Coast, by River Oaks Garden Club. Gardening conditions are indubitably different from my home state of Colorado, and this book was invaluable to me when I moved to the Houston area. The monthly guide offers suggestions and helpful tips for beginning to expert gardeners.
I frequently turn to Jerry Baker's books for gardening advice. The first time I encoutered Texas critters in my garden I checked out Jerry Baker's bug off! : 2,193 super secrets for battling bad bugs, outfoxing crafty critters, evicting voracious varmints and much more!  All of his books offer simple and effective suggestions for combating common gardening problems.
What are your favorite places to visit in Houston? Do you have a gardening book that you can't live without? It would be great to hear what others enjoy.