Came across a fascinating article in Investor's Business Daily on dead tree (see, you accomplished something with that free trial).
The IBD staff compiled evidence of media bias via the various studies on the subject. Here are some of the results:
1. 2005 Study -- Every major media outlet except The Washington Times and Fox News Special Report leaned to the left. The furthest left (by a long shot) was the Wall St. Journal news division (as distinguished from their conservative op-ed group). Other groups leaning left were all the network morning news shows (with one exception), NPR Morning Edition, and the major newsmags. The closest to the center were Aaron Brown's Newsnight (now canceled, hmmm), PBS Newshour with Jim Lehrer, and ABC's Good Morning America. The authors of the study hailed from UCLA and Univ. of Missouri.
2. A 2004 study showed that nine of 10 major newspapers are more likely to portray economic data as negative if a Republican is president.
3. A 1996 study showed only 7% of Washington correspondents voted for George H.W. Bush in 1992, nearly half as many as voted for Bush in ultra-liberal Berkeley, CA.
4. A 2004 NYT story found only 8% of Washington correspondents thought Bush would be a better president than John Kerry.
UPDATE: I should have mentioned that I found item 2 particularly interesting. For years, I have had the sense that Republican economic data has been spun in a negative light relative to when Democrats are in office. Looks like the old intuition was right.