Time ago, I found a experiment with particles on the site "asluv.com".

I like it, but it was a little slow, so I decide to change the code a little, and just avoiding the use of sprites, I got a great improvement on the speed.

This AS3 experiment uses a BitmapData to determine whether the particles should change their speed in function of the background color of the bitmap.

There is a GlowFilter and BlurFilter applied to the particles, to create a nicer visual result.
Playing just with the filter, we can get very diferent and nice result.

Click here to see the demo. ( requires flash ).

Download: ActionScript 3.0 source files and demo