So, I've been looking into some good type of monitoring service, and I've found out about Souptime.net. Which service do you use? Things why I mainly like Souptime: - Fast - Cheap - SMS notifications Also, it offers nice monitoring for HTTP services, where it checks for status codes..
We use Cacti and Nagios. They both offer notifications and great resources for troubleshooting as well as looking back on graphs when things come back online.
If you have an iPhone get a free account on Pingdom, you can monitor one website free and get direct notifications to your iPhone app.
I use the free version of Pingdom as well to send downtime alerts to my cell phone, so far it's been very useful (and accurate). Some other popular ones: SiteUptime Mon.itor.us Host-tracker Site24x7 ServiceUptime