The description of dhtmlxMenu :: DHTML/JavaScript Menu - Play With New Friends
dhtmlxMenu provides simple Ajax-based solution for web navigation. It allows to create attractive dropdown menus within minutes. dhtmlxMenu can load its content from XML so it can be easily changed without reloading. The menu features cross-browser/multiplatform compatibility, rich client-side API and customizable icons (with javascript or xml). It supports vertical scrolling of items and several buttons types. Available under GPL.