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.
Sucuri - Website Protection, Malware Removal, and Blacklist Prevention
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Amazon CloudFront - Amazon CloudFront is a content delivery web service.
Better Uptime - We call you when your website goes down
CloudFlare - Cloudflare is a global network designed to make everything you connect to the Internet secure, private, fast, and reliable.