Closure Tools : The Closure Compiler, Library, Templates, and Stylesheets help developers create powerful and efficient JavaScript.
DOMAssistant : The modular lightweight JavaScript library, with CSS selectors, event handling, AJAX and complete Unicode support
JavascriptOO : Every javascript project you should be looking into.
With examples, categories, install commands, CDN links, project and author stats, and more.
SoundManager 2 : Using HTML5 and Flash, SoundManager 2 provides reliable cross-platform audio under a single JavaScript API.
Wave.js : Audio visualizer library for javascript. Create dynamic animations that react to an audio file or audio stream.
A simple library for handling keyboard shortcuts in Javascript.