For the purist:
http://www.grc.com/menudemo.htm
Absolutely no JavaScript, pure-css only - and works with virtually all browsers.
A little tweaking can make them look as good as the fancy menus (jQuery, etc.)
But we have also used jQuery, YUI! and others. YUI! has great accessibility options built in, if that's a requirement for JavaScript-powered menus.
--
Andrew
