Richard Venancio

This plugin used to get de sub menu refers the current item menu, and show this with a menu, for exemple a sub menu left.
Supose you have a big main menu, and this have a lot submenus, so, to show yours submenus in a side of your site, you create one new menu in wordpress for each submenu you have, and create codes to define which submenu you show, according the location in hierarchy’s menu you are.
This is very tiring and biggest, for just show the submenu, then this plugin do all things for you, but don’t create any menu, it just get the submenu according the main menu.

RVSubMenu

This plugin used to get de sub menu refers the current item menu, and show this with a menu, for exemple a sub menu left.

jessejd

Enhanced Custom Menu replaces the ‘Automatically add new top-level pages’ feature of wordpress 3.0 with an enhanced version automatically adding subpages to their respective place in your custom menu’s hierarchy. This plug-in allows custom menus in wordpress 3.0 to work like wp_list_pages with the ability to edit the menu from the admin menu editing interface. 
This is perfect for those who would like to automatically add subpages to their navigation menu on publish without editing core wordpress files. 
Enhanced Custom Menu also updates the delete menu item feature, when a page is changed from publish to draft, review, or moved to the trash, the respective menu item is removed. If the page is later added re-published the menu item will come back.
In 0.2 pages that have sub-pages are not removed from the menu if they are changed from published status. This retains the structure of the menu.
Note: You must have custom menus enabled, running wordpress 3.0, and turn on ‘Automatically add new top-level pages.’

Enhanced Custom Menu

This plugin alters the custom menu auto-add function allowing subpages and delete menu item after un-publishing a page.

RVSubMenu vs Enhanced Custom Menu