Get a list of every Bad Religion song. Close your eyes and drop your finger on the page. You'll probably find a good one under your finger. Theres a song from the average "No Substance" album called "The State Of The End Of The Millenium Address" which is essentially Greg Graffin simply talks over the top of a simple riff which is nicely written.
I do have to say that I love "ifwhiteamericatoldthetruthforonedayitsworldwouldfallapart" by the Manic Street Preachers as a very good anti-America/anti-racist/anti gun song though. Not that the Manics don't have a nice collection of political songs to go with it.
Other than that, Refused, International Noise Conspriacy, Dead Kennedys and even Jello Biafras post-DK material are all ripe for good political songs. Anti-Flag to be honest have to be one of the worst political bands I have ever heard. Their music is catchy, but the lyrics are fucking awful.