Also review plugins with these tags:
Allows you to make your content accessible only to registered and logged in users.
Restrict (protect) categories on a user-by-user basis. Useful for restricting Categories seen when writing a post.
Adds new admin menu for setting category visibility settings for the front page, searches, feeds and archives.
Control the number of post in various pages in your blog. Plugin supports tagging features introduced in 2.3.
Provides a way for admins to block certain e-mail addresses from being used during registration.
Puts blog into demo or maintenance mode except for authenticated users.
Only shows Wordpress content to other users if they meet certain access criteria.
Allow users to ban IPs addresses from the admin panel.
Freezes the passwords for specified user IDs. Ideal for setting up a public sandbox server where you do not want anyone to change the public password.
Allows admin to hide parts of posts from users who are not logged in by use of <!--hidethis--> and <!--/hidethis--> HTML comment tags. Compatible with Wordpress 1.5 and later.
Wordpress usernames are case sensitive. Many people on the Internet are used to case-insensitive passwords, where "Caroline" and "caroline" refer to the same account. Insensitive plug-in takes care of it. Sensibly.
'Sticks' a page to the front of your blog, and can restrict certain IPs access beyond that.
Remove posts from child categories under your (presumed parent) category archives.
Very simple plugin to allow only users at a minimum level to post on a category. You can define a minimum level for each of your categories through the admin panel.
Limits the categories that are displayed on the edit post page for users who do not have a high enough user level.
Allows you to make your blog temporarily unavailable to your visitors with a custom message. It is still accessible by the administrators and logged in users.
Allows you to restrict access to posts based upon the user level. Only registered (and logged in) users with a level greater than or equal to the post level may view the post.
Allowing multiple authors on your site while still maintaining editorial controls.
Puts a password specified in the protect-old.php file on every post but the latest published one that doesn't already have a password.
Allows only registered users to view your blog.
Allows the banning use of specific email addresses and domains from user registration.
Restricts access to the comments section of the admin panel
Comprehensive control of reading and editing access: default WordPress roles work as is by default, but you define additional role restrictions and assignments by page, post or category. Can assign roles by user, WP Role group or custom-defined group. Features include Attachment Filtering, Hidden Content Teaser, RSS Filtering, Pending Revisions. Actively maintained and forum-supported. For WP 2.5 to 2.9.
Allows admin to restrict individual posts or entire categories of post to only those users who are registered and have logged in. Compatible with Wordpress 2.0.x. Future support for Wordpress 1.5 might come in a future release.
Trims the passwords to eliminate accidentally entered ( usually during copy/paste) spaces and other characters (tabs and double quotation marks like this one: “). Cuts down on user frustration.
Automatically trims the usernames to eliminate accidentally entered ( usually during copy/paste) spaces, tabs, colons, and double quotation around the usernames. Seriously, there are real people who got shaky hands due to their old age, physical exertion, excessive use of recreational substances ( = too much coffee), or just the plain excitement of seeing your blog. Do not lock them out!
Allows exclusion of categories from your front page, archives, and feeds.
Allows the specification of a theme for visitors vs. a theme for administrators facilitating the testing of a theme before making that theme visible to visitors.
Extends user profiles to include admin-defined attributes, and provides for category access controls with per-user granularity. ==ViewLevel2 :Lets you hide specific posts from unregistered users or users below a given user level.
WP-Members is a plugin to restrict WP content to be viewable by registered site members. It is designed to work “out-of-the-box” with no modifications to your theme, but also to be scalable for those that want to customize the look and feel, or want to restrict only some content. Can restrict both posts and pages.
Assigns a site-wide password to all WP powered posts and pages. Allows exclusions to the password requirement. Nice when you can't get at .htaccess and don't want to manage users.