This post was published more than a few years ago (on 2006-07-11) and may contain inaccurate technical information, outmoded thoughts, or cringe takes. Proceed at your own risk.
This is an amazing java applet that analyzes your iTunes music collection and creates a short audio "signature" file from snippets of your favorite songs. Pretty clever.
The only downside seems to be it's not able to use songs you've bought in the iTunes Music Store, due to the DRM.
I encourage you to check it out--- here's mine, and a list of the contents.