Well, this could be a never ending list, but here are some of the animals I think would have (or can) make for the line:
Dolphin, Chimpanzee, Komodo Dragon, Cheetah, Cardinal, Ant, Bee, Ostrich, Stag Beetle and Wolverine.
I think that those 10 are all common animals that the average kid would be able to recognize if they were integrated into the line.
Some more 'obscure' animals that I think would be cool are: Red Panda (a totally different animal from the Giant Panda), Gibbon, Ring-tailed Lemur, and a Yellow Jacket.
Just to name a few...