I've read Dogs Never Lie About Love and The Intelligence of Dogs, both of which I enjoyed a lot. I have also read all the James Herriot books multiple times, they are still some of my very favorite books. To this day I can laugh and cry as I read his experiences.

There are plenty more but either I can't remember titles or authors or both at the moment. The two Chicken Soup books on pets are very good though, I think the first is Chicken Soup for the Pet Lover's Soul, and the second Chicken Soup for the Cat and Dog Lover's Soul. They aren't JUST about dogs, but they have so many wonderful stories.