PageSpeed Ninja - One-click page speed boost for WordPress
Website Grader - Grade your website's strengths and weaknesses in seconds.
Website Speed Ranker - Compare how fast your website loads vs your competitors
Smaller - Make your websites load faster
Treo - Treo is the page speed monitoring tool that helps your customers from obtaining a faster web experience.
Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting