S Hetjens

This plug-in restricts access to blog and feed. All anonymous visitors will be forwarded to the login page of WordPress 
before accessing the blog content. If access is restricted, rss and atom feeds will be disabled, too.
The feed can be activated as a private feed for each user. Every user will have a unique feed url to access it. That 
url is based on the username and an md5 hash of the hashed password stored in database. This plug-in will modify all 
by wordpress inserted feed urls to the user specific ones. But be carefull. If you content is confidential you should 
not activate the feed. There is no way to check which services are reading (and maybe publishing) the feed’s content.

Hetjens Registered Only

This plug-in restricts the access to blog and feed. Visitors need to login before accessing the blog. It offers a private feed for every user.

slickorange

This simple plugin enables you to set up different access codes or passwords that enable users to be added to specific WordPress Roles or Press Permit (http://presspermit.com/) permission groups.
Simply go to Settings -> WP Access Codes to create and manage your codes.
Use the [wp-access-codes] shortcode to display the input field in the frontend.
More features planned! Please make your feature requests in the support area or send a mail to info@slickorange.co.za

WP Access Codes

Assigns a WordPress Role or/and a Press Permit Group to a user based on a predefined access code they enter.

Hetjens Registered Only vs WP Access Codes