Cascading Vertical Side Bar Menu

I am looking for a good looking vertical cascading side bar menu widget. I know I can add custom menus that are page specific, but what I want is a cascading menu like the main menu acts. Custom side menus stack the menu items but do not hide sub menus. I have a new site that will have about 50 sub menu tabs under 5 main categories. We do not want all menu items to show in a stack because the page will run too deep.