Add Conditional Statements to your post content e.g. IF the user is logged in display "Welcome back!"

This plugin enables a custom theme when the administrator is logged for a safely testing.

The simplest way of controlling who sees what in your posts/pages. Restrict content to logged in users only (or guests, or by roles) with simple shortcodes.

Allows you to close your site to non-logged in users, by redirecting them to the login page, displaying a message or a specific template file.

File Proxy lest you protect / restrict access to a specific embedded file making sure users are logged in before they can download any files.

Generate an extra variable to secure your wp-admin access thru a simple variable name & hash passed in the URL

Private Files makes sure only logged in users can see images and file attachments.