Google Web Toolkit
Google Web Toolkit
http://code.google.com/webtoolkit/
DOJO
DOJO
http://dojotoolkit.org/
Ajax Toolbox
Ajax Toolbox
http://www.ajaxtoolbox.com/
JQuery
jQuery
http://jquery.com/
MochiKit
Mochikit is a highly documented and well tested suite of javascript libraries that will help you get things done, fast. it takes good ideas found in python, objective-c, etc. and adapts them to the crazy world of javascript.
http://mochikit.com/
Script.aculo.us
Script.aculo.us
http://script.aculo.us/
QooxDoo
Qooxdoo is an advanced open-source javascript-based gui framework. it helps you to implement ajax-enhanced web 2.0 applications - easier than ever before.
http://qooxdoo.org/
Moo.fx
Moo.fx, a superlightweight javascript effects library
http://moofx.mad4milk.net/
Yahoo! User Interface Library
Yahoo! User Interface Library
http://developer.yahoo.net/yui/