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.
Simple Ops - Simplify website performance and uptime monitoring with alerting, ssl check, chrome ux metrics, multi locations
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Momento - Momento is a unique diary/journal writing app for iPhone & iPod touch, which provides a quick...
Better Uptime - We call you when your website goes down
Monitorly - Get real-time alerts for your SSL Expiry