jMenu is a jQuery plugin that enables user to create horizontal drop down menu with unlimited sub-menu effects. Besides jQuery, it also requires jQuery UI and supports all the effects of this library (like fadeIn or slideDown).
Extremely easy to implement, JMenu is a way to display and manage a multi-level menu on your site. It is fully configurable, customizable and lightweight CSS (7K for the uncompressed version).
Website: http://www.msconcept.fr/jMenu