The Enterprise theme has two menu bars. Enterprise is the only one I know of that has two menu bar locations that you can actually put pages on. The default behavior of the lower category menu is to show the 10 most popular categories on your blog and no more. Though you can customize what's shown there with Custom Menus. You can create a new custom menu and assign it to the secondary menu location and then add and arrange as needed.
According to the following article, Motion and Titan also have two menus:
http://wpbtips.wordpress.com/2010/06/30/posts-on-pages/ And all themes here will work with the custom menu widget. Motion has a normal menu bar and another one shows categories. Titan, it just adds the categories to the end of the pages menu.