iTunesMouseRemote turns your shiny three-button mouse into a remote control for iTunes. You can activate it by selecting the "iTunesMouseRemote" option from the script menu in iTunes, and press Esc to deactivate it. Basically, it makes your scroll wheel a play/pause button and volume knob, and your left and right buttons into next/previous track buttons. It's somewhat of a proof-of-concept at this point. If you find it useful (I do, especially with a bluetooth mouse), please leave feedback.
iTunes 4 or later, Mac OS X 10.3 or later (may work on earlier versions of each but is untested)