Private WP 2 will make sure people can only read your blog and rss feeds after they log in. Already logged in users will see no difference.

Private WP 2

Makes your blog (including RSS feeds) accessible only to logged in users.

This plugin allows you to easily open and close your website and display a custom message or HTML page when closed.
<ul>
<li>Simple yes/no toggle to open/close your website.</li>
<li>Display your own closed.php within your theme.</li>
<li>Display your own custom HTML markup, pasted directly into the plugin settings.</li>
<li>Display a basic message informing your visitors that your website is closed.</li>
<li>Set paths which bypass the closed page entirely.</li>
<li>Set a bypass GET parameter which will allow anyone you give the URL to to browse the website as normal while the site is closed.</li>
<li>Automatically clears any caches for W3 Total Cache and WP Super Cache.</li>
</ul>

Website Open/Closed Toggle

This plugin allows you to easily open and close your website and display a custom message or HTML page when closed.

Private WP 2 vs Website Open/Closed Toggle