Right outside the west entrance, like one block west and 1/2 block south, in West Yellowstone is a very nice "zoo" showcasing wolves and bears. There's also a nice inside area with exhibits and the usual gift shop.
When I was in Yellowstone fairly recently I saw bison everywhere, deer, elk, bald eagles, otters, coyotes, and other animals I don't recall, but I didn't see any bear or wolves from the roads; we didn't do much hiking to speak of. The bear and wolf zoo, though, was very nicely done if you want to see the live animals up close.