Dilly's wonderful reference is still around. http://redwall.muck.limitless.org/Members/Dilly/Animals for at least basic information on all of the currently allowed species (plus a few others).

As far as size goes, that's really tricky, as BJ wasn't even consistent with this himself from book to book. About six months ago I was working with someone else to try and come up with a relative size reference for all the MU species. The trouble is, of course, that everyone seems to have a slightly different opinion, even if you discount birds entirely from the list. Anyways, if I were to make a chart based on both the books, real life sizes, and the way things are RP'd on the MU, it would go /roughly/ something like this:

(Pygmy Shrew, Sparrow) - (Small rodents - shrew, mouse, vole, ect.) - (Large rodents - Rats, squirrels) - (Hedgehogs, Moles, rabbits) - (Most common mustelids - weasel, ferret, stoat, ermine, etc.) - (Cats) - (River Otters, Martens, Hares, Foxes) - (Sea Otters, Beavers, Wildcats) - (Badgers, Wolves, Monitor Lizards, Horses)

Obviously, that's not all the species (I didn't even try with birds, birds like owls can have /huge/ size ranges, even in the books). Also, most of the size differences are bound to be gradual. Sure, a badger is going to be much larger than a shrew, but not /that/ much larger than a wildcat or a sea otter (recall that Lord Brocktree and Ungat Trunn went nearly head to head with each other. Also that Finbarr, a sea otter, picked up Urgan Nagru, a fox who was large enough to wear a wolfskin, and had enough strength to smash him into a tree. Things like that.)

I'm sure there are plenty of other views on species size. Nothing official for the MU has been laid down, and BJ certainly never has either.