Wave.js : Audio visualizer library for javascript. Create dynamic animations that react to an audio file or audio stream.
jsmad : jsmad is a pure javascript MP3 decoder, based on libmad, with an ID3 decoder written from scratch.
Band.js : An interface for the Web Audio API that supports rhythms, multiple instruments, repeating sections, and complex time signatures.
RAWGraphs : RAW is an open web tool to create custom vector-based visualizations on top of the amazing d3.js library.
Primarily conceived as a tool for designers ...
Javascript Sound Kit : The Javascript Sound Kit is a wrapper around the ActionScript Sound Object, it makes it possible to use the Sound Object in Javascript the same way yo...
dancer.js is a high-level audio API, usable with both Mozilla's Audio Data API and Webkit's Web Audio API with flash fallback, designed to make sweet visualizations.