Seconded. This is one of THE best monsters. I'd also like to mention Gelatinous Cubes.
There are some that are hilarious, but not really GOOD. Duckbunny, Armadillephant, Giant Space Hamster, really any from here.
I love these double-animals. I've introduced a few of my own making in my games. There was a really memorable one with a group of aquatic ogres herding Squeep (Colossal squid/sheep) with their trained Whogs (Sperm whale dogs).