Actually floatzel is not a rodent. It's an otter, which belongs to the mustelidae family, like weasels or ferrets.
Skunks (family mefitidae, I think)vbelong to order carnivora, not rodentia, so they're not rodents either. In fact, a skunk is more related to a bear or a dog...
Zangoose is a mongoose, which is not a rodent at all.
There should be more rodent pokémon, I'm sure...
A beaver is a rodent, so bibarel is one of them. Pikachu is also suposed to be a mouse or something like that. If you consider marill a water mouse, it's a rodent too. Plusle and minum could be mice too, but I think they look more like rabbits (which are in the lagomorpha order, so not rodents).