[Plugin: WordPress CSS Drop-down Menu] Very Intuitive and Flexible

Sleek and functional. I was even able to make it work with other CSS / JavaScript systems, OR I could use it with the excellent standards compliant CSS file it ships with. Great admin panel features, easy to understand, and works as advertised. No problems at all working with other plugins, and I have a LOT of them.

http://wordpress.org/extend/plugins/wordpress-css-drop-down-menu/