StatusNotify - StatusNotify monitors the status of 250+ cloud services.
Is It Down Right Now? - Network & Admin
IsDown App - Monitor all your cloud services status pages in one place
UPDOWNtoday - UPDOWNTODAY allows you to check whether the website is down or not.
DownDetector - A simple service to tell you whether a website is down.
Site Down - Site down outage and downtime reports from SiteDown.co