Speed testing a website
There are two tools I use:
1) http://www.webpagetest.org/ – this is an excellent resource to test page load times across geographies. It also has a suggestion feature to automatically identify performance issues with the page. Some of the things quickly identifies are image sizes, unnecessary headers, CDN usage, script/css/html size, etc
2) Firebug – this is an add-on plugin to Chrome and Firefox. It allows you to measure and break down page load times to the local system. It has a clean and neat UI with a timeframe view which gives a pretty good visual representation of the page load process.
Although they have common features I believe both tools are useful in their own aspects and a must have for any web developer