I think it would be cool to have Earth, Fire, Wind, and Water element pets. It doesn't matter what species you use it on.
I also think it would be awesome to see some Greek god/goddess type pets. For example: A set of store pets could contain a Zeus dog, Hera dog, Poseidon dog, Hades dog, or whatever Greek god/goddess you choose. You have already used Cerberus as a store pet, which Cerberus is a guard dog in the underworld.
If you need more explaining or need ideas of what to make an animal look like, I am more than willing to help.
I hope my suggestions are acceptable..