Keep in mind that I haven't read a lot of the classic animal books like Because of Winn-Dixie, The Underneath, anything by Kate DiCamillo, etc. And it's been forever since I've read Shiloh, A Cricket in Times Square, The Incredible Journey etc. So I'm just using recently read stuff for this.
Also, I don't have any live-action movie or TV animals because they never look right to me. Animals can't act. So usually they just have animals sitting there and then add a lot of inaccurate sound effects, like cats yowling when they're supposed to be calm and friendly. A friendly meow is different from a distressed yowl, you guys.
5. Smut from Dairy Queen. Because her name is Smut! She was named after "corn smut" which is blackish and sometimes found in ears of corn. Her fur looks like that. Also because she's just a pet, no supernatural powers, except making D.J. feel better, which is what pets do.
4. Pongo from One Hundred and One Dalmatians (movie). The scene where he's trying to find a mate for himself and Roger, omg, hilarious.
3. The Colonel from The Hundred and One Dalmatians (book). In the movie he's kind of a bumbling idiot, but in the book he's a stately old dog who teaches the puppies military strategy. Puppies! Military strategy! He promotes people every time they do something awesome, and then at the end of his chapter after chasing after the inept dog thieves and biting them as hard as he can, he promotes himself. Love it. Honorable mention: Cruella de Vil's cat, who helps them get revenge on Cruella at the end because Cruella drowned her kittens.
2. Sirius, the Dog Star, from Dogsbody by Diana Wynne Jones. Because, the entire book. I mean, just read it. Honorable mention: Tibbles the cat, who helps him out of more than one scrape.
1. Buttercup from the Hunger Games trilogy. Not only is he a fucking badass and THE REAL STAR OF THOSE BOOKS, he's responsible for making me cry, every single time I read the trilogy. Those of you who have read it may know the moment I am talking about. I just lose it.
More honorable mentions: Hedwig the owl, Pounce the magical kitty (who may or may not be a god) from the Beka Cooper books, Chester the paranoid cat from Bunnicula.