IsZDown - Monitor the errors and status of the most popular websites and apps. Check whether they are down right now or not.
Is It Down Right Now? - Network & Admin
IsItDown RightNow - "Is It Down Right Now" monitors the status of your favorite web sites and checks whether they are down or not.
UPDOWNtoday - UPDOWNTODAY allows you to check whether the website is down or not.
Pingbreak - Pingbreak is an original and free monitoring service.
IsThisSiteDown.org - Free tool to check whether a site is down just for you, or for everyone.