Web Audio Vocoder
This application (also shown at I/O 2012) implements a 28-band (actually variable number of bands) vocoder - a "robotic voice" processor. It's a pretty complex audio processing demo. It also supports live input, and has several controls exposed; it supports MIDI control over the pitch and other parameters.
Check it out, feel free to submit issues or requests, fork, submit pull requests, etc.
The live app is at http://webaudiodemos.appspot.com/Vocoder/index.html.