The iTunes3 documentation reveals that pressing '?' while in Visual mode brings up some visuals generator options: 'F' for frame rate info and capping, 'R' for cycling the config settings randomly, etc. (press '?' again to see the second help page).

What's not documented is that you can cycle through the config settings at will, not just randomly. There are three config variables with many possible combinations. I don't know the proper names, but I've dubbed them Wave, Flow and Colour.

• Wave: How the waveform appears on the screen. Press Q and W to rotate settings.
  
  
• Flow: The way the waveforms form patterns. Press A and S to cycle.
  
  
• Colour: The colour settings for the pattern. Z & X to cycle these.

If you press 'C', you can see the values for each of these items change in the upper right corner of the screen as you cycle through the various options.

Used in conjunction with 'M' ('Select config mode'), it is possible to freeze a custom visual, instead of progressing to other styles. Coupled with fullscreen mode and screen capture, this is a nice way to get some funky desktop patterns!