Edit: I've entered in the LED contest, Hurricane Lasers, and Fix & improve it contest. If you like this, please vote.
Using an Apple Pro speaker, I made a flashing RGB LED iPod dock for about $35.
I recommend reading the entire 'ible before starting. Also, note that the volume is control from the iPod.
It consumes minimal power in shutdown mode, and is controlled by a Teensy
This took me ~3 days to build, and you should know how to solder pretty well before doing this project.
The enclosure looks amazing when lit, it is really fun to watch it.