This plugin does a lot of things related to private and password-protected posts and pages:
* Optionally adds private pages to wp_list_pages(), wp_page_menu(), and the Pages widget
* Provides a separate wp_list_private_pages() tag (a clone of wp_list_pages() that accepts all the same arguments) and private pages widget
* Specifies private categories, in which all posts will automatically be set to private
* Lets you to change the "Private:" prefix on private post/page titles
* Lets you to change the "Protected:" prefix on password-protected post/page titles
* Lets you to choose which user roles can read private pages and posts
http://wordpress.org/extend/plugins/private-suite/
(A pre-1.0 release has been in the repository for a while, but was never announced outside a small group of testers.)