css3-mediaqueries-js : make CSS3 Media Queries work in all browsers (JavaScript library)
Ember.js : A JavaScript framework for creating ambitious web applications
script.aculo.us : script.aculo.us provides you with
easy-to-use, cross-browser user
interface JavaScript libraries to make
your web sites and web applications fly.
Rickshaw : Rickshaw is a JavaScript toolkit for creating interactive time series graphs.
jsmad : jsmad is a pure javascript MP3 decoder, based on libmad, with an ID3 decoder written from scratch.
A library to generate PDFs in client-side JavaScript.