I should put in a plug for my personal friend Jinx the Cat, the co-star of the Freddy the Pig books.
YESYESYES, Simon’s Cat!
Also love Hobbes. If he were a person, I’d marry him. Wait… he doesn’t have to be a person; I’ll marry him anyway.
ETA: Oh, yeah, the Kliban cat, a helluva nice animal frequently mistaken for a meat loaf.
Bastet.
Take that, theists!
Jeez, I have got to dig out my Cordwainer Smith collection and read through it again. What a writer he was!
Baron Humbert Von Gikkingen and Moon/Muta/Renaldo Moon from Whisper of the Heart and The Cat Returns. Loads of cats in the latter…
Desdemona, Cicero ’ s Cat (from “Mutt and Jeff”)
Moushi, the Van Daans’ cat in the play * The Diary of Anne Frank. *
When our school put this play on, the part of Moushi was played by Sir Gregory, a silver Persian owned by a member of the Thespians. He was very calm, although some cast members thought he might meow ad-lib. He earned 3 Thespian points. 
Mr. Jinks from Pixie and Dixie cartoons.
Pyewacket hasn’t been mentioned yet.
Post #10
A yard customer of mine, herself from Thailand, once had a Siamese cat she named Pyewacket. He had a sister named Tiffany.
Crookshanks. (Hermione’s cat, if anyone wonders. And another Greebo-like personality).
Lt. M’Ress
No one has mentioned my nomination: that irresistible Frenchman: Henri. Of all the videos, #2is my favorite.
Jennyanydots, Mr. Mistoffelees, Mungojerrie & Rumpleteaser, Skimbleshanks, Grizzabella, Macavity, Bustopher Jones, Old Deuteronomy, and the Rum-Tum-Tugger.
(I’ll leave it to you to decide if I am a fan of T.S. Elliot or Andrew Lloyd-Webber.)
This is also my vote.
You need to see THIS! 
Heathcliff. Mel Blanc voiced him in the cartoons.
Bucky Katt’s acquaintances (does he have any friends?) Chubby Huggs, Mac Manc McManx and Foodar
Scratchy (from the Itchy and Scratchy cartoons)
Stimpy
Wiley Catt from Pogo (although technically he’s a bobcat)
Ruff from the Ruff & Reddy cartoons (yeah, the cat is the one named “Ruff”)
Bumped.
Just found a treasure trove of Kliban cat T-shirts here (including one with the mousie song): http://www.crazyshirts.com/category/men/kliban-cat.do?page=all
TS Elliott’s Jellicle Cats
Aslan, from the Narnia books
(apologies if already mentioned)