Looks nice, haven't tried it yet but the rainfall diagram reminded me of Billy's Phreaknic talk.
There are several tools that can generate Waterfalls:
IBM Page Detailer has probably been around the longest. Its free, runs locally, and is a little clunky. Also, [PRNT SCRN] + [CTRL] + V is the only way to export images.
Firebug has had a waterfall diagram for a while now, but the timing is not very accurate. The 1.5.x code base (in beta but downloadable now) fixes most of these issues and supports the HAR export format which Httpwatch supports as well.
AOL Page Test is free, runs locally, and is good.
I used WebPageTest.org for my phreaknic diagrams which is simply a number web hosted version of AOL Page Test scattered around the world.
Pingdom and a few other places do waterfalls as well.