http://www.leveltendesign.com/blog/superuser/add-menu-sub-navigation-sidebar-block
Add menu sub-navigation as a sidebar block in Drupal
I am currently on a project that requires a 2-level drop down navigation and a sidebar block that displays the pages in the current section. This is not the first or second time I have used this recipe so it's time to share. This block can be used to display other pages in a section.
