[JonnieCache]

I'd just like to chime in with another vote for soundflower. It's useful for any number of things, I have recently used it to pass youtube videos through VST plugins to clean up the audio, and to make Cave Story, a somewhat old game, work with my external soundcard. You can also use it as an alternative to those ripoff "record your audio output" programs.

It is made by the fine people who produced Max/MSP.