Neil Sperry's Complete Guide to Texas Gardening by Neil Sperry (1991), but more to do with the fact that I checked it out from the library twice, renewed it twice, and mostly read it while I was eating my cereal in the morning.
This is a good basic reference to Texas gardening -- particularly the extensive encyclopedias of flowers, plants, shrubs, and trees, complete with photographs, identifying traits, and general care. This second edition was published in 1991 and could probably stand an update to incorporate some more organic and water-conscious gardening techniques. Still, there is a lot to love here and I could see myself buying a reference copy of this book someday as my gardening aspirations grow.
Joolie, and beyond her tutelage, most of my techniques have been trial and error. Still, I have managed to grow edible food from seeds in dirt I put into a container by myself and I'm pretty excited to have gotten this far. Maybe in the spring I'll go crazy and try some herbs!