Actually, I have a friend who used to breed gerbils; he has 17 right now and used to have like 23. From what I heard from him, it's pretty easy, and they tend to be cleaner than mice. Also, in the petstore that I work at, a gerbil has already given birth to about 6 babies.

I might try breeding some gerbils, mostly just to see what it'll be like. I don't really need that many, either, so it might work out.