A good friend of mine from college, Andy, has been programming music visualization software for many years now. He started SoundSpectrum, a company based on his work. Recently another friend of mine, Anton, joined him. They just released their newest version of G-Force on June 8, 2005.
A little bit of my work is included in the new version. I wrote the line drawing algorithm that it now uses. The new line drawing algorithm produces much smoother lines. Before the edges of lines were jagged and bumpy. Now they are smooth and anti-aliased. I get nice credit in the G-Force version history
If you haven't used G-Force, you should try it. It works as a plugin to a bunch of music software including Microsoft Windows Media Player, Apple iTunes, Musicmatch Jukebox, J. River Media Center, Cowon jetAudio, Nullsoft Winamp, Real Player, foobar2000, MediaMonkey, Quintessential Player, and XMPlay. It can also be used standalone and reacts to whatever music is playing on the computer speakers. The G-Force music visualization effects are just stunning. I can sit there and watch them for hours.
You could also try out WhiteCap - is a 3-D wireframe spectrum analyzer music visualization plugin. It's quite cool too, but not quite as nifty as G-Force
One a more personal note, SoundSpectrum has a page up where they have photos of the staff. Anton's photo is particularly bad. It looks like a mug shot. So much so, that I edited it in The Gimp to make it really look like a mugshot. Maybe he'll change it now.
-- Sorry Anton, it's for giving my coworkers the picture of me in the wig.