I think ungulates like deer and horses would be neat. Why? Well, it's just nice to be playing as a lion on a large savanna, and you see zebras and gazelles in the distance. Or, if you're a wolf trying to get back to your pack, you might see a deer through the trees in a forest. I think it would just flesh out the game a bit more, so it's not just all cats and dogs running around. Besides, plenty of people have already said that they want horses.