Visualizations literally let you watch your music move. Windows Media Player comes with over 30 visualizations, and you can download more from the site below. Once you've downloaded a visualization, you can find it in your Windows Media Player under the 'View' pull-down menu. Or, when you're playing your music, you can scroll through the visualizations on your computer by using the arrows in the status area of the player.
More info:
hxxp://windowsmedia.com/9series/Personalization/visualizations.asp?page=4&lookup=Visualizations