To encourage the integration of broadband and information technology into local economies, the National Telecommunications and Information Administration (with some help from Stamen) now provides an exploratory tool for broadband in your community:
The National Broadband Map (NBM) is a searchable and interactive website that allows users to view broadband availability across every neighborhood in the United States. The NBM was created by the National Telecommunications and Information Administration (NTIA), in collaboration with the Federal Communications Commission (FCC), and in partnership with 50 states, five territories and the District of Columbia. The NBM is a project of NTIA's State Broadband Initiative. The NBM will be updated approximately every six months and was first published on February 17, 2011.
There's a lot of data to look at, but you can search for the city or zipcode that you're interested in, and get information on what's available, as shown below. You can also see how your city compares to other locations in the country.