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.
FastNetMon - FastNetMon is a very fast DDoS analyzer with sflow/netflow/mirror support.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Arbor - Easily manage product development
Better Uptime - We call you when your website goes down
Corero - Real-time, high-performance, automatic DDoS attack protection, on-premis and in the cloud, with comprehensive attack visibility, analytics, reporting.