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 - Tracking website updates, automated and simplified
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Reddit Check - A tool to check if a URL is on Reddit and going viral
Better Uptime - We call you when your website goes down
FeedMail - FeedMail sends you updates from your favourite websites directly to your inbox (or filed nicely into a label of your choice).