The Communications Workers of America, i.e. the union that represents many of the workers at the ILECs, Verizon, AT&T and Qwest, has a great website called Speed Matters. I don't think we see eye to eye on the solution, but we agree there is a problem: The US is falling farther and farther behind in broadband access when compared with the rest of the world.
Among other things, Speed Matters offers a speed test, asking first for your zipcode and email address. They have been accumulating data for a while now, at least since I last mentioned them in February.
Now Speed Matters has added an interactive zipcode by zipcode account of Internet access capabilities across the US. It's also available as a report in pdf form.
But averaging by zipcode doesn't tell the real story!
I do a lot better at my home: 20 Mbps down and 2.7 Mbps up vs. averages for my zipcode of 1596/ 562 kbps up.
I do a lot worse at my summer camp in Maine where averages for the zipcode are 729/ 135 kbps but I'm beyond the limits for DSL and 1100 feet from the nearest cable TV line and so remain limited to ~26 kbps using a dialup connection.