You didn't mention anything about holistic health...but, these are my favorites.
Healing Pets with Nature's Miracle Cures by Henry Pasternak, DVM, CVA
He really has some good information..thanks bari for sending this
The Holistic dog book by Allegretti & Sommers
Great for quick reference and for learning the basics of acupressure
Herbs for Pets by Wulff-Tilford, Tilford
Great reference guide for herbs and conditions
I 3rd the recommendation for Dogs by Raymond Coppinger. I ordered it by mistake many years ago...found it a good read and great reference. I learned a great deal about predatory motor patterns, how purebred dogs were created etc. Very interesting.