UptimeRobot - Free Website Uptime Monitoring

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.

Distill Web Monitor - Distill is a web monitoring tool. It can monitor RSS feeds, a webpage or a part of webpage. Alerts in the form of pop-up, audio or emails can be received.

RapidSpike - RapidSpike is a reliability, performance and security monitoring service for transactional websites. Using next-generation synthetic monitoring & deeper than ever before data, RapidSpike is for businesses serious about protecting their online revenue

Wachete - Track web page changes and get notified. Free Sign-up. Have all data in one place