Accessible Website Menu: Ultimate Drop Down Menu by Brothercake:
"Ultimate Drop Down Menu v4.0 [beta] by Brothercake

UDM is a lightweight and accessible javascript menu, which provides useable content to all browsers - including screenreaders, search-engines and text-only browsers. But accessibility shouldn't mean compromise, and so UDM has a sophisticated range of design and usability controls, many of which are unique to this script.… "

http://af.brothercake.com/dropdown/