Take me back! Not just to those groovy days when the light organ was the hottest party starter, a breakout of the LM4970 used to be stocked by SparkFun back in the day. We have played with them and they are too cool to end up out of rotation. It is essentially a PWM driver with audio signal control. You can give it stereo or mono line feed, and it will output 3 channels (low, mid, high) of PWM. Communicate through I2C interface for audio controlled output, or select from 7 colors.