For dressage bookworms, you can learn more about other trusted dressage literature here.
A Journal of Four Dressage Horses from Birth through the First Year of Training
Balance and Bodywork for Horses & Riders by Sylvia Loch covers unmounted ground exercises in understanding gravity and balance that can be transferred to the saddle.
In this three-DVD set, we see dressage Olympian Klaus Balkenhol working with many horses, from foalhood to maturity, and learn about his contemporary approach to horse training based on classical methods.