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.
Ahrefs Webmaster Tools - Optimise your website and get more traffic from Google.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Dareboost: Website Speed Comparison - Check how fast your website is against your competitors
Better Uptime - We call you when your website goes down
Treo Site Speed - Find out how fast your website is for real users