Bias Beyond a Reasonable Doubt: Yes, the media are overwhelmingly liberal.

The Weekly Standard ^ | December 13, 2004 | Robert J. Barro

[Dog Gone]

Liberal think tanks included the Center on Budget and Policy Priorities (88), Citizens for Tax Justice (88), the Consumer Federation of America (82), the Economic Policy Institute (80), the National Organization for Women (79), and the NAACP (75).

You know, I've never considered NOW or the NAACP to be "think tanks."

[AFPhys]

While looking for more articles referencing this study, I came across:
http://www.frontpagemagazine.com/Articles/ReadArticle.asp?ID=14020

" Militant Islam is one big counterexample to the Left’s facile belief in the ‘equality’ of all ‘cultural perspectives.’ If the liberal media were to report candidly on the Jihadists, they would have to acknowledge that culture is not airy and light, but serious and heavy and sometimes evil. Such an admission would call multiculturalism itself into question, and the Left can’t do that. Multiculturalism is today a pillar of the liberal faith. And who’s going to knock the faith?"

I think that this article really does a good job of explaining just where some of the media bias stems from.

[HoustonCurmudgeon]

I thought about that when I read it and believe organizations, rather than think tanks would have been a more accurate description.