Three Plugins To Monitor Site Uptime

Adam Burucus has published his overview of three different WordPress plugins that can be used to monitor a websites up-time. It seems to me that Pingdom is the most popular player in this market based on their history and how many major websites I’ve seen mention their service. At least by his overview, Pingdom is the only one out of the three that provides mobile alerts which is a deal breaker for me. I have my phone with me everywhere I go so that would be the perfect option to be notified of when a site goes down.

How many of you are using some sort of up time monitoring service?