Option-Click Sound Menu to Change Input Source
Here’s a cool trick I just learned. If you want to quickly change your sound input device, simply Option-Click the Sound menu at the top of your screen to enable an alternate menu pulldown list of input devices. For an audio geek like me this is a lot quicker than launching into the System Preferences and adjusting from microphone to line-in audio source. As far as I know this is new to Mac OS X 10.6 Snow Leopard. Enjoy!

This is not new to 10.6 as I am running 10.5, but is very handy none-the-less.
I would recommend you check out SoundSource from RougeAmoeba, if you haven’t already! It’s basically this same menu item, but, on steroids.
-NeyeTr0