Yahoo! UI Library (YUI)
Ext JS - JavaScript Library
A library of DHTML and Ajax scripts - DHTMLgoodies.com
Dynamic Drive DHTML(dynamic html) & JavaScript code library
Prototype Window Class : Introduction
The Dojo Toolkit | The JavaScript Toolkit
jQuery
mootools - home
Prototype JavaScript framework: Easy Ajax and DOM manipulation for dynamic web applications
script.aculo.us - web 2.0 javascript
Orangoo Labs - GreyBox
Slimbox, the ultimate lightweight Lightbox clone · digitalia.be
LightWindow Demo