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.

Scott Nelle

Uptime Robot uses the uptimerobot.com API to display log messages relating to a site’s uptime. You must have a free uptimerobot.com account to get any use from this plugin.

Uptime Robot

A dashboard widget for monitoring your uptimerobot.com log messages

PG Monitor vs Uptime Robot