SevOne - SevOne provides network managers with monitoring, troubleshooting, and performance reporting capabilities.
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.
Flowmon - Clever Network Monitoring and Security Solution based on NetFlow, IPFIX and Network Behavior Analysis
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Nagios Network Analyzer - Nagios Network Analyzer is a netflow analysis, monitoring, and bandwidth utilization software.
Better Uptime - We call you when your website goes down