I was looking for a way to switch between my line out options on my Mac Pro. I wanted to be able to switch between my headphones and my table speakers. So i stumbled across this little app that adds an icon to my menu bar with a bunch of switching options. You can pick it up at http://www.rogueamoeba.com/freebies/ The company makes awesome apps like Airfoil and Nicecast. Also the pong screensaver is great!