A friend of mine had the idea to make ordinary lightbulbs react to music, for a large event he was organizing. We put our heads together and a month later we ended up with these.
In each box there is an atmega328 microcontroller, an msgeq7 "spectrum analyzing" IC, two shift registers, two transistor arrays, and five strands of rgb led strip. The spectrum analyzing IC allows the boxes to react to 7 different frequenty bands, but only the lowest two (63hz and 160hz) proved to be visually interesting.
The music we tested them with on the video was most obnoxiously dynamic music we could find. Might not suit a lot of ears, but it suited the lights. We still have to make a better video though.