Steve

This plugin uses a custom field to allow sub titles/headings to be added to any post type, including pages, posts and any public custom post type.
The custom subheading field is re-positioned so it is directly below the main title when editing.
Updates to your theme templates may be required in order for you to output the subheading values, please refer to the Installation instructions.
By default subheadings are also appended to RSS feeds and the admin edit post/page lists, these options and more can be modified via the settings page.
Following a plugin review by Alison Barrett (WordPress.com VIP) a number of improvements were introduced in version 1.7.
Languages: Also available in Brazilian Portuguese (Português do Brasil by mauriciomesquita).

SubHeading

Adds the ability to easily add and display a sub title/heading on any public post type.

hildende

With installing this plugin you add functionality to <code>wp_nav_menu()</code> to show 
only children of the current page or start with a specific navigation level.

Child Navigation

Adds support for child navigation to wp_nav_menu()

SubHeading vs Child Navigation