1. The Other End of the Leash, by Patricia McConnell: certainly not a dog training book, but more of a people training book. This one challenges you to take a step back look at your behavior as your dog might, from her end of the leash, and consider the effect that behavior might have on your dog.
2. On Talking Terms with Dogs: Calming Signals, by Turid Rugaas: recently reviewed, I feel that this book gives concise descriptions of behaviors that dogs exhibit when they're uncomfortable or unsure of a situation, that an owner might misinterpret as disobedience, stupidity, or worse. Dogs don't speak English; this book helps you learn to speak dog.
3. Bringing Light to Shadow, by Pamela Dennison: This book is the journal, with notes, of a woman who adopts a people aggressive, extremely reactive dog from rescue. And, using positive techniques (as opposed to physically punishing or coercive ones), "fixes" him. It's a painstaking process, and the book is very informative about the strategies used, and overall, highlights that dogs take PATIENCE. And that behaviors can be unlearned.
4. The Thinking Dog: Crossover to Clicker Training, by Gail Tamases Fisher: since I didn't clicker train from the get-go, Elka is a "crossover" dog, technically. "Clicker dogs" are encouraged to think and problem solve; "traditionally trained" dogs are to watch their humans for a cue. Of course, you want your dog to look to you for decision making purposes, but the joy I've seen Elka take in what I want when we work with the clicker is a sight to behold. And I've clicker trained her to look to me when she's unsure of things.
5. Playtraining Your Dog, by Patricia Gail Burnham: I had a lot of fun reading this book, which does give pointers for training specific behaviors. Burnham includes plenty of anecdotes about her dogs and others, and, as the title suggests, tries to make training play for the dog, and thus fun!