Suprvise is a real-time health monitoring and errors tracking dashboard.
WebGazer is an uptime monitoring platform that checks if your website is up as it should be and notifies you if anything goes wrong
Monitority - Simple website monitoring service (sms/email alerts)
UptimeRobot - Free Website Uptime Monitoring
Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Oh Dear! - Website monitoring, without the hassle
Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.