CSSMenu top + 2 columns
This is a drop-down menu that is using only CSS (although some Javascript is required for Internet Explorer 6, note: IE6 will not let you use 2 of these menu types in a template at the same time as the second one will fail to open). It can be either vertical or horizontal.
The code we have inserted in the template that this page is using is simply {menu template='cssmenu.tpl'}. You style the menu in the stylesheet Navigation: CSSMenu - Horizontal or Navigation: CSSMenu - Vertical for the vertical CSSMenu.
But to be on the safe side, copy this style sheet and attach your new style sheet to the template instead (and make your changes in your new style sheet). Then you can always revert to the default style sheet if something goes wrong.