Roku

<p>This plugin makes uploaded files only accessible by logged-in users.</p>


Uploads Protector

This plugin makes uploaded files only accessible by logged-in users.

fpoller

<p>Gives the following options for making the WordPress installation more private:</p>
<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.

Uploads Protector vs Private WP suite