I have always been a big fan of Frederic Remington and Robert Vavra. I don't know how many times I checked out Masterworks from the public library. It's an expensive book to buy second hand, unfortunately.
Crown Jewels of Thoroughbred Racing by Richard Stone Reeves
A lavish volume of famous Thoroughbreds by the renowned artist.
Horses of the Sun by Robert Vavra and William Shatner
It's hard to resist the powerful photos of Robert Vavra. Horses, particularly Andalusians, run free in natural settings, a great gift!
Unicorns I Have Known by Robert Vavra
This book enchanted me as a child, I often wondered where he found the unicorns! Quotes accompany breathtaking photos.