I'd go with B. Kliban's "Mysterious little creatures, aren't they?" except that it doesn't make sense without the cartoon, and I can't find a link. In the cartoon, a man says the line while contemplating a cat sitting inscrutably on the floor, not realizing that two other cats are frolicking behind him on the back of the couch and making faces.
Years ago in Zimbabwe, it was common for the locals to "earn a crust" by "looking after your car" while it was parked. The theory was that they would feed your parking meter and prevent any thieves from breaking into or making off with the car. One of these guys was a character called George who had a gammy leg and used to hobble around. I asked him one day: "George, you can't walk very fast, how are you going to stop thieves taking my car?" He fixed me with a knowing look. "Sir" he said, "There is more than one way to kill a cat!"
ďI shall sit down,' replied the cat, sitting down, 'but I shall enter an objection with regard to your last. My speeches in no way resemble verbal muck, as you have been pleased to put it in the presence of a lady, but rather a sequence of tightly packed syllogisms, the merit of which would be appreciated by such connoisseurs as Sextus Empiricus, Martianus Capella, and, for all I know, Aristotle himself.'
Your king is in check,' said Woland.
Very well, very well,' responded the cat, and he began studying the chessboard through his opera glasses.
And so, donna,' Woland addressed Margarita, 'I present to you my retinue. This one who is playing the fool is the cat Behemoth...Ē
? Mikhail Bulgakov, The Master and Margarita
Well, a few I can think of...
"Not enough room to swing a cat" hopefully that one's self explanatory.
"dead cat bounce" is a small, brief recovery in the price of a declining stock.
"cat that got the cream"
Interestingly in South Gloucestershire (my home Shire) there are a few Cat related place names... "Cattybrook Road" and the more worrying name "CatBrain Hill"; I'd hate to think if that hill was man (or cat) made.
And then there is that lovely phrase "The catbird seat" which is nowhere better used than in James Thurber's story of the same name:
The wikipedia entry is also worth a read if you are curious (but remember, curiosity killed the cat... ;-)