Racso and the Rats of NIMH (Rats of NIMH, #2)
by Jane Leslie Conly, Leonard Lubin
I vaguely remember the first and last books in this trilogy, but for whatever reason this was the one that I liked the best. I was really into the rat society, complete with rat university, rat anarchoterrorists, rat inventors, teenage rebel rats, etc. It's been a very long time since the last time I read it, though.