jQuery Menu is a solid menu system that helps creating dropdown, iPod drilldown and flyout styled navigations easily.
The Jquery menu system uses a hierarchical unordered list for creating the menus & sub-menus.
It is ready with ThemeRoller which makes it very easy to customize the look and has ARIA (Accessible Rich Internet Applications Suite) support.
With various configuration options & ease of use, jQuery Menu is definitely a very helpful solution for creating menus.