Just learned about Compete.com, which compares traffic on websites, at a seminar today held at the National Press Club library, from audience member Josh Kaufman, at an event hosted by librarian Beth Shankle. You can enter any URL, and compare it to two others...
Also learned about popurls.com, which as the man sitting next to me explained, is made for "pack journalism." And EC2 (and here at Amazon) cloud computing, used to put together sites like the New York Times archives' TimesMachine.
You can find links to all the sites we learned about at the Press Club's del.icio.us site.