Thursday, September 1, 2011 at 7:52PM iTunes Visualizer plug-in for Mac OS X. Made this a while back. It's really hard to screencapture this visualizer, but there is a lame attempt:
Better to get the real plugin and run (if you have a Mac!)
Download: SoundThing.bundle.zip
Another iTunes visualizer is Klangfarbe, it has a better screencap video and more install instructions.
Saturday, May 8, 2010 at 1:34PM 
This plug-in is still in beta and does not work with all graphics cards, please let me know if it works with yours!
In my first visualizer - AlphaOmega - I tried to envision a form or geometry for the music. This one, Klangfarbe deals more directly with visualizing the current audio as colors, hence the name which is German for "timbre" but also means "color of the timbre" or "color of the sound".
License
Free for personal, home, non-commercial use. For other use, please contact peder /dot/ norrby (at) gmail /dot/ com. This free software is provided as is, with no guarantees whatsoever.
Download
TrapcodeKlangfarbe_BETA5.zip
It has a few settings:
Press "m" key to toggle modes, there are three modes and the first two are animated (they change slowly over time)
Press "f" key to change particle feather / out-of-focus effect.
Install help
1. Unzip the .zip file (double click it) if needed.
2. Place TrapcodeKlangfarbe in the iTunes Plug-ins folder. Normally this is:
(username)/Library/iTunes/iTunes Plug-ins
.
3. Restart iTunes
.
4. In the menu select View>Visualizer>Klangfarbe.
5. Play a nice tune.
6. Hit Command-T to start the visuals!
Friday, February 19, 2010 at 11:19AM
Audio-driven animation. Trapcode Particular 1.0 was used (yes, that was the initial version, this clip was made about two years ago). Awesome in its simplicity.
The song is "Light Rain" by Plaid ©2001 Warp Records Limited.
Monday, February 1, 2010 at 1:38AM Trapcode Particular, AE Waveform. Music and Graphics by Peder Norrby
Thursday, January 28, 2010 at 12:43PM
ABSTRACT MINIMALISM
I tried to envision the music as colors and moving shapes. I use Trapcode Sound Keys and Trapcode Form in Adobe After Effects.
Music by Kymatica
Continuation of vimeo.com/8515375