I have long wondered how there came to be this "well-known" liberal bias that I keep hearing spouted out as a talking point. Last I checked, Fox News, the Washington Post, and the New York Times were all part of the "MSM," not to mention "Meet the Press."
Glenn Greenwald did an outstanding job of covering this myth here.
My take on it is that several years ago some stories that some influential people on the right considered important were overlooked by the media because the majority of Americans didn't care (if people don't care, it's not newsworthy). They then decided that this was a product of "liberal bias." If it's not this, then it could be a product of Rush and his machine creating this environment of a split nation.
But what to do with all the favorable reporting of President Bush during his first 2 years in office (ignoring the dangerous situation he and his policies were creating), as well as all the negative reporting regarding President Clinton, President Obama, and other such situations? That's simple - you ignore it - and focus instead on piddly stories that mean little, if nothing, to bolster your claim. If you repeat a story often enough, it becomes true, apparently.