Maurice, from The Amazing Maurice and his Educated Rodents - also by Terry Pratchett.
Tabitha Twitchett - from Beatrix Potter.
Speaker to Animals
Heathcliff
Bagheera and Shere Khan from The Jungle Book.
Definitely Havoc, from George R.R. Martin’s Tuf Voyaging. Or Dax, a big, sleepy long-haired cat with a psionic link to Tuf, warning him when others are untrustworthy or about to attack. Tuf also has cats named Mushroom, Havoc, Suspicion, Doubt, Hostility, Ingratitude, and Foolishness. Here he is with some of them: http://georgerrmartin.com/gallery/art/tuf05.jpg
I’ve also always had a soft spot for McDermott, the titular feline in Robert Lawson’s Captain Kidd’s Cat, a semi-retired, somewhat surly pirate’s cat with a ring in his ear and a taste for rum in his daily dish of milk: https://catunes.files.wordpress.com/2012/04/1344204.jpg
HOBBES! (You people do realize tigers are cats.)
Also Krazy Kat. Who went on to inspire both the above AND the below…
The Cat in the Hat!
Fritz the cat.
How could I forget Mister!
Also, Arabella, Jenny, and Mr. President from the children’s book Jenny and the Cat Club, and Snowball (I - V) from The Simpsons.
Also his cousin, Tigger.
Cringer
Lion-O
Hobbes
For the slightly larger felines, I’m also fond of the much-put-upon Jorin, from Hodgell’s Kencyrath novels.
Jorin is a hunting ounce (a domesticated cat about the size of a serval) psychically bonded to a roving disaster disguised as a young woman. Blind from birth, he uses her eyes to observe whatever mess she’s gotten them into and occasionally deigns to let her use his senses of smell and hearing. Of course, since she’s rarely looking at him when things get busy, he’s forever getting his paws and tail stepped on, being tripped over, bouncing off walls, and so forth. Also, his mistress makes a very restless pillow. What’s a cat to do?
Ah, you’ve chosen the infamous censored strip… 
(Some editions changed “beaver” to “marmot.”)
Snuffles from Pears Before Swine.
Dr. Henry Metzger, from Thomas Perry’s heist novel “Metzger’s Dog.”
I liked him so much I named our cat after him.
Lots of my favourites have been mentioned, so I’ll add some Kiwi cats …
Scarface Claw - the toughest tom in town From Hairy MaCleary (Lynley Dodd)
with an honorable mention for Slinky Malinki
Horse - from Footrot Flats (Murray Ball)
We were naming our new cat just a few weeks ago, and my son and I ran through a bunch of Pratchett names, and completely missed Greebo.
Ah well, we settled on Gimli
Mewsette and The Money Cat from “Gay Purr-ee.”
The indisputable leader of the gang–Top Cat!