This is a pretty nice one, but I'd like to find one that supports multiple levels.
Here's an updated version: http://www.nickrigby.com/examples/dropdown3/index.htm
Vertical version: http://www.nickrigby.com/examples/dropdown4/index.htm
http://www.brainjar.com has a pretty nice menu bar too and explanation of how it was made.
I like the ones at nickrigby.com.
This gives the control of the menu style to CSS, meaning it will allow the css-appfuse project to be more flexible.
Created new CSSListMenuDisplayer and added examples for both horizontal and vertical menus.
Tested with IE on Windows XP and Firefox/Safari on OS X.