Fairness & Accuracy In Reporting). Conservatives are just as convinced that because the substantial majority of journalists are political liberals, their reporting tilts to the left, especially when it comes to topics such as religion.
Unfortunately, it is fairly easy to "prove" one side or the other. All you have to do is cherry-pick those news stories that support your case and ignore all other evidence to the contrary. What is needed is a systematic evaluation of the media based on either a randomly selected set of news reports from media outlets or on all news reports from media outlets over a given period of time. Alas, those kind of data are hard to come by, which is why it is so easy for both liberals and conservatives to dig up evidence supporting their point of view.
That said, methods for the analysis of texts have improved substantially in recent years, and as a result a number of interesting studies have been conducted that are helping to sort the wheat from the chaff. These haven't settled the debate, of course. A lot more work needs to be done, but they have certainly helped scholars get a better handle on this debate.
Media bias is the topic of a recent Freakonomics podcast, "How Biased Is Your Media?". It nicely summarizes a number of these new studies and presents some interesting statistics, such as which media outlet is the most conservative (it isn't FOX news but FOX isn't too far behind the leader) and which is the most liberal (you'll be very surprised here). One thing these results highlight is the divide between the news room and the editorial board. One would think that at a given outlet the opinions of the two would correlate highly. Sometimes they do, but sometimes they don't.
The podcast also discusses studies that have identified the most liberal and most conservative members of Congress along with the most popular phrases employed by Democrats and Republicans. All in all, it is a very interesting podcast.