Someone asked about mice a couple of weeks ago, and got a lot of good responses, including a lot of humane and cat-safe suggestions:
The most important thing is figuring out how they get in and seal off their entry spots with steel wool.
Mouse traps or the tent style glue boards. Traps in my opinion are a faster more humane way to kill. Just prevent the kitties from getting to the cheese, or peanut butter on the traps, by covering over the traps with cardboard tent or boxes so the cat cannot access the traps.