This one is really cool:

You ever hear a song and don't know what song it is?
Tunatic is a small (free) program that you install on your computer (PC and Mac) that can listen to a song and identify what song it is.

Tunatic has a very simple interface and all you need to use it is a microphone and an Internet connection. Tunatic hears some music and quickly identifies what song it is.

Very nice!