Ah yes, Sonic Visualizer is an incredible tool. Despite the name which might sound like merely a trippy thing to watch, it can be used for extremely serious work, such as reverse-engineering world music scales, tuning instruments, figuring out and annotating the notes in a song, etc.

Note #1. The VAMP plug-ins seriously kick up the power of Sonic Visualizer and that they are open-source and used in the also amazing online tool Chordify which is found at http://chordify.net

Note #2. Chordify is a neat tool which automatically extracts the chords from any youtube video you point at it. It's free, but if you pay an additional 50 cents or so, it will send a you a rudimentary MIDI file with the chords in it. It's been worth it for me several times already.