...and read up on the companies to avoid.
This is infinitely more important and impactful than just calling up a radio or TV station and complaining about hearing Rush or seeing O'Reilly spew their BS. The stations don't really care that you don't like what you are watching or hearing, they only care that you're watching or listening. (Are you listening, Media Matters?)
However, if you call one of their sponsors and let them know that you will not be spending any money at their store because you know that part of your dollar will go to the radio or TV station who will then use that to help pay for Rush, or Hannity, or O'Reilly, or Alex Jones or any of the other right-wing nuts to tell lies about you and your country. And you don't even have to go into any detail. Just let them know that you don't want your money going to those people and so you will not be spending any money with their company. They will be the ones who then call the station to pull back their support if they get enough calls saying they're going to be losing money for sponsoring the wing-nuts.
More details on upcoming posts, but this site is a good place to start.
This is America. You vote with your dollars!