I'd like to be able to stream Pandora to an AirPlay or Bluetooth speaker while watching a video or using an app that has sounds, routing all the non-Pandora sounds to the internal speakers.
I used Soundflower for something similar I think. I have not used it since Lion but might be worth investigating.
Some programs allow you to do this if it's programmed into the software, although that doesn't help you. For example, Teamspeak 3 will allow the output to go through your headsets, but leave everything else on the Mac going through the speakers.