This is one of the best ways to create a pop-up menu that I've found yet. It is done with simple HTML and the CSS isn't that complicated either. It proivdes very clean pop-up menus and can be done either vertically or horizontally.
In this tutorial we will be creating a horizontal menu. The only draw back to this method is that IE 6 and lower doesn't support the ul li:hover CSS style. We will cover how to work around that in the tutorial though.