"The National Broadband Map is a tool to search, analyze and map broadband availability across the United States. Created and maintained by the NTIA, in collaboration with the FCC, and in partnership with 50 states, five territories and the District of Columbia."The image above is static. To access the zoomable map, go to this link.
Via The Centered Librarian.
Update 2020: The source for the image has not surprisingly undergone linkrot. Those interested in the subject matter can find updated information at this link.