WebPagetest - Run a free website speed test from multiple locations around the globe using real browsers...
HttpWatch - HttpWatch: The ultimate HTTP Sniffer for Chrome, IE and iOS
Website Speed Test by Pingdom - Pingdom is a website performance monitoring software.
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.
SEO PowerSuite - Get all SEO tools in one pack - download free edition of SEO PowerSuite and get top 10 rankings for your site on Google and other search engines!
Yellow Lab Tools - Website test that checks performance and HTML, CSS and JavaScript quality.