Mirte

If, for example, your clients want to be able to “turn off” their website for a while, so they can work on new 
content or features of their website, but you don’t want them rummaging through the WordPress Settings pages to do so, this plugin might be something for you.
This plugin creates a very simple little widget for your WP Dashboard, from which the website can turned to / out of maintenance mode.
Activating maintenance mode will display a maintenance mode page with explanatory text for your visitors. Logged in users will be able to view the website as they normally would.
The plugin will automatically create a <code>maintenance.php</code> file and add it to your <code>/wp-content/</code> directory. Customize this page to change the appearance and text of the maintenance mode page.
Known bugs 
* Right now, this plugin will not work on certain servers (like Antagonist.nl) because of a permissions issue.

Dashboard Maintenance Mode

Adds a nifty widget to your dashboard from which you can put your website in maintenance mode.

Pippin Williamson

Easily put your site into maintenance mode with this plugin so that you can perform updates. The plugin works by taking a selection of IP addresses and comparing them to the visitor’s IP address.
Users whose IP addresses match those specified in the settings page can view the site normally. Users who do not have IP access are directed either you a WordPress page (which you pick), or to any external url.
It’s extremely simple to use:
<ul>
<li>activate the plugin</li>
<li>go to the “Maintenance Mode” settings</li>
<li>check the “Enable Box”</li>
<li>enter the IP addresses that should have access</li>
<li>choose whether to redirect non-authorized users to a page or url</li>
<li>choose the page or enter the url</li>
</ul>
Once your site is ready to be made available again, simple uncheck the “Enable” box.

CGC Maintenance Mode

Good options, no check if the URL is on the same domain which causes redirect loop.



Almost there

This plugin allows you to put your site into maintenance mode, by allowing only users with specified IP addresses to view the site.

Dashboard Maintenance Mode vs CGC Maintenance Mode