One of the many uses for a particle system plug-in like Particular is the ability 'visualize' music through the formation of particles. I've seen some amazing examples over the last few months and this is one of my experiments called Red Smoke.
Watch Sample Video
Download Project (CS4 & Particular 2 required)
About this Project:

After I extracted the keyframes from the audio amplitude, with this technique, I linked the particle birth and the velocity to the sound intensity with expressions. This made the bursts of particles shoot out farther for the louder notes and tighter for quiet parts.
The original comp was actually black with colorful particles (See sample) but I wanted to create something a bit more unique so I inverted the luminance and colorized part of it so it would be more dramatic Red on Black.
To get away from the sandy look of small particles I used a vector blur set to "Perpendicular" to blend it more naturally.
There are about a 2 million particles per frame so the render took about 4 hours but I lowered the rate while working to speed things up. I also offset the final audio a few frames to match the visual since the birth causes a slight delay.
Side Note: Harry Frank did a pretty in-depth tutorial at RGTV.
If you have any questions, post them!