Two Political Science professors studied the mainstream media over the course of the last 2 years, and concluded, yes, the Mainstream Media is liberal, and shows it in their news.  They were careful not to include editorials which are by definition biased reports.  But the conclusion, while in itself not astounding, did produce some surprising results. 

The study showed that the Wall Street Journal and the Drudge report were liberal!  But in the case of the Drudge report, they attributed that not to Drudge's writings, but to the other Mainstream articles the site carries.

And while NPR was found to be liberal, it was not as liberal as some would think.  And of course to no one's surprise except maybe members of du.org, CBS, The NY Times, and LA Times were deemed the most liberal (behind the WSJ).

The study looked at the last 10 years of reporting and used, of all things, the Americans for Democratic Action's tally sheet to rank the sources.  The ADA is a very liberal outfit, so at worst, this may have tended to slant sources to the right.  But even with their (ADAs) scale, 18 of 20 of the outlets studied scored left of center.

So now the debate is settled to the surprise of very few.  The MSM is liberal, and thus the reason that the alternative media is so strongly conservative.  Nature abhors a vacuum, and there has been one on the right for too many years when it came to honest reporting.