This is a nice little site that I've had bookmarked over the years. It has a nice list of animals as categorized in the middle ages, both real and mythical (well, perhaps not mythical from their point of view, as most have some sort of basis in reality).
Not only does it list them, it gives descriptions based on period sources, often times has a period illustration, and even discusses the symbolic/allegoric nature of the animal. Its kind of a "cliffs notes" type of website, but overall pretty well done.
