Federal Communications Commission has a large amount of information on the radio and television stations broadcasting in the U.S. as well as a number of stations in other countries in the Western Hemisphere. Wolfram|Alpha computational knowledge engine has recently added this data.
"Try out the call sign for your favorite radio station. You might be interested to know who holds the license for that station or find out that it's being broadcast from that antenna you drive by on your way to work. The local map not only shows you the location of the antenna, but is also zoomed in to show the approximate listening area. How tall is that antenna? Wolfram|Alpha has the answer, as well as a lot of other technical details about the station antenna," stated Wolfram|Alpha.