PeoplesGeek

Monitoring services like www.siteuptime.com or www.montastic.com require a page on your website to monitor.
This plugin provides a virtual target for your monitoring services that does not invoke other plugins (specifically avoiding the Google analytics plugins so that your statistics are not skewed by monitoring calls) 
The two targets provided for the monitoring service are:
<ul>
<li>monitor.htm – via .htaccess and does not use WordPress (but does use PHP)</li>
<li>monitorWP.htm – via WP and so tests the Database etc is working</li>
</ul>

PG Monitor

A virtual target file to be read by monitoring services instead of using a static HTML page.

siteimpulse

Super Monitoring is an external web application for monitoring website uptime and its basic functions. 
This plugin integrates Super Monitoring interface into WordPress administration panel so you don’t have to log in to supermonitoring.com separately to see your reports or update settings.
Super Monitoring features 
– checking your website every minute 
– detecting different kinds of failures 
– using a worldwide network of monitoring stations to avoid false positives 
– measuring response times 
– content checking 
– web form testing 
– file integrity monitoring 
– instant email & mobile text (SMS) alerts 
– unlimited event history 
– API.
In order to use the plugin you need an account at <a href="https://www.supermonitoring.com/" title="website monitoring" rel="nofollow ugc">www.supermonitoring.com</a>. 
You can sign up for a free trial <a href="https://www.supermonitoring.com/sign-up" title="sign up for a free trial account" rel="nofollow ugc">here</a>.

Super Monitoring

Monitor your website uptime and basic functions with www.supermonitoring.com and access your reports and settings directly in your WordPress panel.

PG Monitor vs Super Monitoring