Oklahoma State University
Oklahoma State University: Breeds of Livestock Horses
For a very good primer on horses, visit this site. It contains an alphabetized listing of different types of horses, and the pages include the history of various breeds and their physical features.
American Museum of Natural History
American Museum of Natural History: O Logy: Beautiful Breeds: Appaloosa
Description and detailed illustrations and of the Appaloosa, with answers to questions about its spotted coat.