There are infinitly under rated bands. It's especially hard to rate a some of these bands in the first place, since they're just not as capable as many bands that are complete crap.

I think though, a notably under rated musician in general is Tim Kasher. Between Cursive and the Good Life, he has shown an amazing range of abilities. His voice has a complex tone to it, unlike any one else, and his songs are stories with the detail of the best novel. If you're into the writings of Bukowski, or other such writers, you'd really like Tim.