Visualping - Visualping is the easiest to use website checker, webpage change monitoring, website change detector and website change alert software of the web. Read more about Visualping.
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.
Wachete - Track web page changes and get notified. Free Sign-up. Have all data in one place
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Update Scanner - Update Scanner is a Firefox extension to monitor web pages for updates.
Better Uptime - We call you when your website goes down