Netumo - Ensure healthy website performance, uptime, and free from vulnerabilities. Automatic checks for SSL Certificates, domains and monitor issues with your websites all from one console and get instant notifications on any issues.
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.
Umso - The Website Builder for Startups
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring