CloudFlare - Cloudflare is a global network designed to make everything you connect to the Internet secure, private, fast, and reliable.
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.
SiteLock - SiteLock software provides advanced website security, daily security scans, web app firewall with a CDN to deliver content more securely.
UptimeRobot - Free Website Uptime Monitoring
Amazon CloudFront - Amazon CloudFront is a content delivery web service.
Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.