1. PageSpeed (http://pagespeed.googlelabs.com/)
Google Page Speed test generates a score out of a maximum of a 100 for your webpage. It can also analyze performance of the webpage when viewed on mobile devices. Along with the score, PageSpeed generates suggestions of how to improve your site’s performance. I’ve found that PageSpeed often generates a large amount of false positives, so I would take these suggestions with a grain of salt.
This is my favorite tool to use. WebPagetest is a tool that was originally developed for internal use by AOL but later open-sourced in 2008. It allows to check performance of your site from various geographical locations, using different browsers (IE7,8,9 and Chrome).
Gomez provides a free tool to check how long it takes to load your website from various geographical locations. It measures characteristics such as DNS lookup time, connection time, first byte interval, content download, etc. It doesn’t provide any recommendations but it can be used to diagnose front-end bottlenecks.
5. Browser Shots (http://browsershots.org/)
Finally, performance may depend on the browser and OS you are using.
This site allows you to check how your website will function when viewed on a variety of browsers and OS platforms. While the Browser Shots site won’t help you analyze the bottlenecks, you will be able to see how large the file size is across various browsers, how long it took to load, and if the site looked corrupted.