The new Dreamweaver CS3 comes with a Spry menu widget, which is probably the easiest to use. You could download a demo here: http://www.download.com/3000-2048_4-10701454.html

jQuery has some really cool plugins, which include menu related. http://docs.jquery.com/Plugins

Or use some not so new codes from dynamicdrive.com: http://dynamicdrive.com/dynamicindex1/index.html