fpoller

Gives the following options for making the WordPress installation more private:
<ul>
<li>Protect content from being viewed to users who hasn’t logged in</li>
<li>Disable all feeds</li>
<li>Only serve uploaded files to logged in users</li>
<li>IP address based exceptions for the above options</li>
</ul>

Private WP suite

Adds option in the admin panel for making your blog (including rss feeds and uploaded files) private.

Protect Uploads

The uploads directory is where the files of the WordPress library are stored. Unfortunelty, this directory is not protected. A person who wants to see all your library could list it instantly going to : http://yourwebsite/wp-content/uploads . This plugin will hide the content by adding an index.php file on the root of your uploads directory or by setting an htaccess which will return a 403 error (Forbidden Access).
<ul>
<li>Depending on your server setting, the htaccess option could be disabled.</li>
</ul>
Available languages :
<ul>
<li>English</li>
<li>Français</li>
<li>Español</li>
<li>Italian (thanks to Marko97)</li>
</ul>

Protect uploads

Do not download. The plugin has been changed not too long ago and it now infects your wordpress installation, and possible spreads itself to other sites if you are on shared hosting.

It's a virus

Protect your uploads directory from people who want to browse it. Avoid browsing of your uploads directory by adding a htaccess or index.php file.

Private WP suite vs Protect uploads