NewRelic - New Relic is a Software Analytics company that makes sense of billions of metrics across millions of apps. We help the people who build modern software understand the stories their data is trying to tell them.
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.
StatusPage.io - StatusPage.io is the best way for web infrastructure, developer API, and SaaS companies to get set up with their very own status page in minutes. Integrate public metrics and allow your customers to subscribe to be updated automatically.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Zabbix - Track, record, alert and visualize performance and availability of IT resources
Better Uptime - We call you when your website goes down