Recommended Sites
Animal Diversity Web - Database of descriptions, photographs, and classifications of the world's mammals, birds, amphibians, reptiles, sharks, bony fish, molluscs, arthropods, and echinoderms, searchable by common or scientific name. Some records also provide information on habitats, physical characteristics, food, reproductive habits, and geographic range.
US Fish and Wildlife Service - Information about animals and the Environment.
Primate Info Net - Good deal of scientific detail for a big list of primates.