I think most of the biggies have been mentioned already.
I like the Zombiesmith range for how comprehensive it is for mice - there are a bunch of different mouse troop types, and plenty of sculpts for each. There's a smattering of other critters, but the focus is really on the mice.
Dark Sword has a huge variety of critters, especially lots of frogs, but they're not great for unit-building if that's something that you're interested in. They're almost more like anthropomorphic role-playing characters.
Splintered Light has a huge variety of critters too, are cheaper than Dark Sword, but I doubt they're compatible with most other ranges for size.
One that I don't think got mentioned was Eureka, who has mouse warriors, samurai rabbits, and various frogs. Their frogs are a little less high fantasy than Dark Sword's, with muskets, spears, etc.