Submenu Tree

A little hard to explain this one. Check out this excerpt from the project page:

"Consider using Submenu Tree if you are trying to accomplish any of the following:

• You want to display all of the first level menu items in one location (such as in a navigation bar across the top of the site) and all of the second level menu items or lower to be displayed in another area (such as in a block on the site's sidebar).
• You want to separate the site navigation into multiple levels and present the user with only one level at a time.
• You require the functionality of the core Drupal Books module but find it too limiting or difficult to use.
• All of your content is closely related. You want to display titles or teasers of content at the same level or below the current content.
• You want to display full lists of content that are at the same level or below a piece of content and do not need the complexity of the Views module."