The robot in Lost in Space answers to "Robot", even among those who consider it family and best friend.
The Emergency Medical Hologram in Star Trek: Voyager never found a better name than "Doctor". That's not just Everybody Calls Him "Barkeep": being a Doctor is more than what the EMH does, it's what he is (though he eventually learns to transcend his programming).
"Horse" from Monkey. "Horse" is really a dragon named Yu Lung, but everyone just calls him "Horse".
Power Rangers S.P.D. has Kat Manx, Fowler Birdie, and Sergeant Silverback, who are both aliens that resemble anthropomorphic animals that match their names. Anubis Cruger, who looks like a dog, is also called by the nickname "Doggie" (in Tokusou Sentai Dekaranger, he actually was named Doggie Kruger.) Piggy, however, is a subversion; he doesn't really look like a pig.
Million Yen Women: Shin's housemates can't agree on a name for their new cat, so they decide to take turns calling their name of choice to see to which one it responds. When it doesn't work, they let Shin give it a try. Shin is uninspired and just calls it "Cat", to which it responds.