I have one of these (for human food) and I've been very happy with it so far.
http://www.amazon.com/Black-Decker-E...6886355&sr=8-3


I bought it primarily because it's small, not too expensive but strong enough to handle things like chocolate and walnuts. But I'm sure it would do great to make a paste out of wet cat food too. Just yesterday I used it on some canned diced tomatoes and it basically turned it into very fine tomato sauce in seconds.
It's easy to clean too. You take out the blades and pop it straight in the dishwasher along with the container. The lid (which is basically the mechanics) you can't put in the dishwasher, so that's a bit more tricky, but I've never had problems keeping it clean with some soapy water and paper towels.