Speed testing a website

While developing websites I come across the problem of testing page load times. With Google now bent on giving high priority to websites that are fast it has become even more important to test, debug and improve web page load times.

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