pfSense - pfSense is a free and open source firewall and router that also features unified threat management, load balancing, multi WAN, and more
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.
F5 Advanced Firewall Manager - Stop even the most massive and complex DDoS attacks with BIG-IP Advanced Firewall Manager: advanced data center protection against layer 3–4 threats.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
FireMon - FireMon Security Intelligence Platform delivers continuous visibility into and control over firewall infrastructure.
Better Uptime - We call you when your website goes down