Is the mainstream media fair or biased?

Of course, if we are in America or follow the news there, we are all familiar with the claims of unconscionable political bias. We’re all familiar with Sarah Palin’s constant lambasting of the “Lame-stream Media.” But what is the truth of the situating? Is media biased, and if so, in what direction and why? Who has an opinion founded on facts and not hearsay, political talking points and suspicions? What do such evidence-based opinions say?