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.
AppDynamics - Get real-time insight from your apps using Application Performance Management—how they’re being used, how they’re performing, where they need help.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Opbeat - Application monitoring for developers
Better Uptime - We call you when your website goes down