Source Article:
Getting the Most Out of iTunes 
GimmeSomeTune runs in the background when iTunes is open. It automatically fetches missing cover art and lyrics and adds them to your library of music. You simply start playing a song, and the software does the fetching. You can also have the application display a song’s lyrics in a separate window. If the program can’t find the lyrics, it lets you quickly do a Google search for them. This add-on also supports Last.fm and can function as an iTunes controller. You can download this add-on for free. If you like it, you’re invited to make a donation—a lot of people like it!
GimmeSomeTune Free (donation requested); Mac version only; eternalstorms.at/index2.html;