Following up on yesterday's post, another tool from Stoyan Stefanov's recent post on performance testing tools is PageTest.  From the Stoyan's post:

"AOL's PageTest is an IE plugin but also a hosted service which is a great way to show your boss/client performance details without inconveniencing them with challenging download and installation activities. PageTest gives you a waterfall view of the page load and a checklist of things to improve, plus some screenshots of interesting moments during load and even a video - an excellent view of how the page looks like in slow speeds. The hosted service can show you the dial-up experience in 4 different places in the world.

For some other cool tools, checkout Stoyan's full post.