Site Down - Site down outage and downtime reports from SiteDown.co
UPDOWNtoday - UPDOWNTODAY allows you to check whether the website is down or not.
Is it Down? - Is it down can check if a website is down or is it just your PC that can not access it.
downinspector.com - Find out if a website is down for everyone or just you.
Is it up? - A simple tool to check if a website or ip address is up or down.
IsThisSiteDown.org - Free tool to check whether a site is down just for you, or for everyone.