The iTunes visualizer is based on a visualizer called G-Force which is put out by soundspectrum.com. It used to be that it was available as a free standalone application as well as a plug in for popular MP3 players (it goes back to the days of SoundJam)

Its still available as a free plug in for most MP3 players, but the standalone functionality in G-force is something you need to pay for ($30). However WhiteCap (wire frame visualizer based on the same engine) is still completely free and still comes bundled with a stand alone version.

While I forget if it was possible with the earlier versions (which may still be out there) I know its possible to run the current stand alone versions (whitecap's at least) full screen on a one monitor and still be able to use a second screen to do whatever.

I was having some problems routing audio, but I'm on an odd setup.