Again, not entirely sure what you mean. Adobe offers a Spry Accordion Widget that is basically a series of collapsing panels that I've used in the past to style into a vertical, collapsing menu. Not sure about horizontal though. A default panel/menu item can be triggered to open when the page loads.
I've used the JQuery Superfish plugin which is excellent, requires JQuery free open source framework which is very popular and stable.
"Works with multiple-tiered menus and multiple menus per page. Great for both drop-down menus and and multi-tier horizontal nav bars. Very light-weight and degrades gracefully." - from that page.