An all inclusive web monitoring service.
DownDetector - A simple service to tell you whether a website is down.
Is It Down Right Now? - Network & Admin
Outage.Report - See if your provider or web service is having an outage or it's just you. Post yours and see other's reports and complaints
UPDOWNtoday - UPDOWNTODAY allows you to check whether the website is down or not.
IsItDown RightNow - "Is It Down Right Now" monitors the status of your favorite web sites and checks whether they are down or not.
IsThisSiteDown.org - Free tool to check whether a site is down just for you, or for everyone.