visualization: seeing your music

In the days of modern graphics hardware, fast computers, and enormous digital music libraries, most people have heard of or seen a "visualizer". However, most people using main stream media players such as Windows Media Player and iTunes are missing out on what a true visualizer is. 

Edit (3/26/2012): Granted, this post was written back in 2010. In those days, iTunes was not nearly as cool as it is now. Since my primary computer is now a 2009 MBP, I've found myself using iTunes significantly more. Thei