G-Force

G-Force is a visualization plugin that's compatible with most media players.

G-Force works with plenty of different programs, including iTunes, Winamp, and lesser known programs like Media Monkey. In this case, however, you have the exclusive version for iTunes on Mac OS X.

To enjoy its different effects, all you have to do is click a few options during installation.

With it, you can see all kinds of shadows, shapes, and animations while listening to your favorite songs.

Best of all, it's free.