Harmonic

Harmonic is a simple, elegant, and easy to use lyrics widget for Mac OS X’s Dashboard.

It will display lyrics and fetch an excerpt from them if they are not already stored in the audio file.

Why does Harmonic fetch only the first lines of the lyrics?

Because, of course, of copyright issues. What other ridiculous reason would there be for limiting access to a digital resource?

Unfortunately, that means it won’t change anytime soon. However, at the moment of writing, Maksim Burnin has a fork that fetches all lyrics. You could also check out Get Lyrical, that works great in conjunction with Harmonic! :)

See the official announcement of the lyrics provider and its API policy.