Monitority - Simple website monitoring service (sms/email alerts)
Is It Down Right Now? - Network & Admin
Suprvise - Know instantly when your sites are down.
Is it Down? - Is it down can check if a website is down or is it just your PC that can not access it.
PingPing - A simple tool to monitor your website and SSL
Site Down - Site down outage and downtime reports from SiteDown.co