http://oregonstate.edu/Dept/pol_sci/fac/sahr/ps201/tipsy.pdfis an article by Robert Sahr of Oregon State University examining media bias and double standards as applied to coverage of the Clinton and GW Bush presidencies. It's very up to date, citing several recent studies, and rather discouraging. His "tipsy triangle" consists of the administration, the opposition party, and the media-- who never provide balanced coverage but always tip towards one side or the other. The discouraging side of his argument is that Democrats are hopelessly behind Republicans in their ability to use the media as tools of their opposition to the administration. But one could see a silver lining, which is that if the Democrats can grow backbones the media bias issue could start tilting in their favor.
In 33 pages he gives an excellent digest of thousands of pages of recent research.
CYD