Liberal Media Bias?

It is often lamented that the mainstream media (MSM) has a liberal bias. Recently, examples from the coverage of the presidential campaigns were cited as proof: the generous (in amount and tone) coverage of Obama, and the less abundant and less favorable coverage of McCain and Palin. Some believers have put their suspicions into cartoon form:

While individual anchors and correspondants have their own opinions--whether overt or tacit--they are subjugated to the corporate beliefs. Here's a third cartoon to end with: