GTMetrix helps you figure out exactly how to make your site load faster
Using it is quite simple. Feed it a domain name and GTMetrix loads the page in the background while you wait, and then routes you to a report page.
The report is manager-friendly: It starts out with a summary in huge letters, grading your site like a school paper (A to F). You also get a percentage score. That means your boss doesn't really have to understand anything technical to use this tool -- he just has to run the test and keep pestering you to improve the site until you get an A on both scores (YSlow Grade and Page Speed Grade).
The rest of the report is aimed at the people doing the actual work; sysadmins and webmasters. It contains some very technical recommendations (like "Add Expires headers"), sorted by order of impact upon score. You can click each recommendation to see a complete report showing you exactly what you should change, on a file-by-file basis. It's incredibly detailed.
There are four tabs in this section. The first two correspond with the two test scores, while the third one is a page load timeline (similar to what you get with Chrome), and the fourth is a history. History is only enabled when you're logged on, but if you're serious about using this tool it's a real boon. It lets you see how your site score changes over time (for the better, hopefully).
Bottom line: This is a serious tool for people who care about how fast their site is, and because it's web-based it can be easily used by a team (everyone sees the same thing).