WebGazer - Monitor your website's availability with WebGazer, review its performance and get instant notifications when your website goes down. No installation required and free plan available.
Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
Monkey Test It - Primate powered algorithms that scan your site for common bugs and SEO mistakes.
NIXStats - SaaS monitoring tool for window/linux servers and websites. Think up-time robot but with more features.
BiggerCake - The data tool that Kickstarter deserves
Mention Monitoring Academy - Grow your company with free 8-week course from top B2B SaaS