Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
AWS WAF - AWS WAF is a web application firewall that helps protect your web applications from common web exploits.
UptimeRobot - Free Website Uptime Monitoring
Curler - Dead Simple Free Uptime Monitoring
Imperva Cloud Application Security - Deploy your applications and data where you want. When you want. Imperva keeps them secure in the cloud, on premises, and in hybrid clouds.
Downtime Monkey - Downtime Monkey: website downtime alerts & uptime monitoring worldwide.