Spectrascade is an interactive, tunable WebGL music visualisation project that takes inspiration from both HelloEnjoy’s Lights, and the fun music game Auditorium. (check out both, if you haven’t already!)
The running visualisation can be manipulated using the mouse (both buttons) or tweaked via a myriad of parameters in the control panel.
Interestingly they chose to perform the audio analysis on the server side, with results streamed to the browser for visualisation. I can only presume that this was for performance… and to avoid some of the mess that is cross-browser HTML5 Audio.
The accompanying blog post details their implementation and plans for the future.