Yahoo GUI Library

Yahoo GUI library has a rich set of controls for web development.

“The Yahoo! User Interface (YUI) Library is a set of utilities and controls, written in JavaScript, for building richly interactive web applications using techniques such as DOM scripting, DHTML and AJAX. The YUI Library also includes several core CSS resources. All components in the YUI Library have been released as open source under a BSD license and are free for all uses.”

See the page http://developer.yahoo.com/yui/

You can download the Yahoo UI library from http://developer.yahoo.com/yui/download/

For example, see the Menu control in Yahoo UI library - http://developer.yahoo.com/yui/menu/index.html