Beyond Basic Dog Training
Diane L. Bauman
Here's a book that should be in the library of any competitive obedience trainer. Like the title says, this book focuses on methods of training advanced obedience exercises. While some of the force methods are a little out-of-date, I do still recommend it.
Dual Ring Dog/Successful Training for Both Conformation and Obedience Competition
Amy Ammen, Jacqueline Fraser
This book helps dispell the myth that a dog can't be shown in obedience and conformation at the same time. Plenty of good info for any one interested in training for either type of competition.
Open and Utility Training: The Motivational Method
Wendy Volhard, Jack Volhard
Step-by-step instructions for training higher level obedience using motivational methods.
Successful Obedience Handling : The New Best Foot Forward
Barbara S. Handler
This is an excellent book for anyone new to showing in obedience. Covers all the things you should - and shouldn't - do in the obedience ring.
Competitive Obedience for Winners
Brian McGovern
Great book from this top trainer/handler on how to get to the top.