WebPagetest.org

WebPagetest is one of the best online tools for testing web page performance. It's an open source project that generates waterfall charts and allows you to test on (a limited number of) real devices and browsers, and on a variety of network types and qualities, from various locations around the globe. It's free to use, and you can find it here: webpagetest.org.

WebPagetest also reports the number of requests by type and size, and gives a film-strip snapshot visualization of the render progress. It also allows you to replay a video of the page as it rendered during the test.

In the following image we can see a portion of the performance output for our news page: