GTmetrix - GTmetrix is a free tool that analyzes your page's speed performance. Using PageSpeed and YSlow, GTmetrix generates scores for your pages and offers actionable recommendations on how to fix them.
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.
Website Speed Test by Pingdom - Pingdom is a website performance monitoring software.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
DareBoost - DareBoost is an online tool to test, analyze and monitor your website: speed, SEO, quality, security. All you need for website optimization in a single service.
Site24x7 - Site24x7 offers both free & paid website monitoring services. Monitor websites remotely and receive instant email/sms alerts if your website becomes unavailable. View uptime & performance graphs of your website monitors.