A music visualizer using the Propeller QuickStart, Nick writes;

Video Beats uses a Propeller QuickStart board and a Quick Proto to sample line-level audio (like from your MP3 player) and generate video graphics.  As the audio input changes, new graphics are generated to match the audio.

Seven visualizations are built-in, they will change automatically, or you can switch them manually by using the buttons on the QuickStart.  You can also customize the visualizations to change colors or shapes.

More videos along with assembly and sourcecode @ Gadget Gangster.