It’s nothing fancy (yet) but can easily become very good-looking indeed. Take a look at the tiny Navigation Menu Example and judge for yourself. The example is based mainly on the jQuery plugin: Accordion, and the only main difference is the up and down arrows included in the “slightly modified” CSS.
I’m thinking of implementing this plugin in my new WP theme (which is currently only available in my head) in order to display more info in less space. Another thing worth mentioning is that the code itself degrades beautifully on browsers without Java support as this only results in all menus being shown in “expanded” modus.
Update: Based on user feedback I’ve added an example showing how to add a second level within the list.