What needs to be done to make your site blazingly fast has never been easier. YSqow is a plugin for Firebug released by Yahoo. This tool gives you a good optimization report giving grades from F to A on 22 items from 6 categories: content, cookie, css, images, javascript, and server. In addition to grades and clear advices about what you need to do, it has a few interesting tools such as a compressor for css or javascript files which you can download and put in your site, or the images optimizer called Smushit.