How do you know if your news sources are credible?

With all the contradictory politics out there, how do you know if what you hear in the media is true? What do you do to verify facts? For example, I recently dug beneath the surface of “climategate” and found the damning “hide the decline” statement to amount to a lack of understanding of their data analysis methods. These days I tend to believe NPR, PBS, and the BBC. It has been with tremendous disdain I have watched the development of the Tea Party movement with so many ridiculous “facts” put forth about czars, socialists, facists, Nazis, and the like. How do you combat this mental pollution and remain truthfully informed?