Treo - Treo is the page speed monitoring tool that helps your customers from obtaining a faster web experience.
Website Grader - Grade your website's strengths and weaknesses in seconds.
perf - Perf is a simple app monitoring solution paired with meaningful alerts.
PageSpeed Ninja - One-click page speed boost for WordPress
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 Auditor - The techie's SEO spider: find site issues other tools miss