Private categories is a WordPress plugin by devsector.ch that enables you to make a private category (with login-logout) A login will then appear on the selected category page . Put in this category all posts that should be private not forget to change the status to private. Users must identify themselves to gain access to content
Options: active/desactive privacy, choose category, subscriber can/cant read private posts&pages.
Download and info: http://wordpress.org/extend/plugins/private-category/