Made this simple yet cool led blinker, it just blinks several leds depending on how loud the sound is.
It's pretty neat and blinks perfectly to beats. It looks much better in real action rather than on the video
because of the fps. But you get the idea of how it looks.
I also did a quick tutorial on my blog for this: Stigern.Net » Blog Archive Arduino, LEDs that blinks to the Music! - Stigern.Net