Probably the corporations who own them. Ever since the beginning of what used to be called "the press" (the term "media" did not become popular till the 1950s), there have been accusations of bias by various politicians, advocates, and special interest groups. Some bigots believe a certain group owns or controls the media (some people used to believe it was the Catholics, some still believe it's the Jews, but those beliefs are false. Also false is the belief that the media are controlled by liberals). So, here is the fact: No single entity, person, or religious group controls the media. Different groups-- including powerful business interests, investors, and even some political figures-- are influential in the various media outlets. And as a result, each one can lean right, left, or straight down the middle depending on the political tide, the global situation, the perspectives of the journalists, or what the viewership wants.
Additional input from other contributors:
It is a commonly held belief by many Republicans and conservatives that "the media" are liberal, or that television and newspapers are controlled by left wing liberals while only talk radio and Fox News are controlled by conservatives. However, this is a myth as well as an oversimplification. Let's look more closely.
Television
Most TV news reporters strive to be neutral, and the same is true for most of the news anchors, including those on NBC, CBS, and ABC. Certain TV networks do have an ideological bias-- Fox News is well-known for holding conservative views while d MSNBC has a number of left-leaning commentators as well as some neutral news reporters. Some critics claim CNN and BBC are also liberal, but they tend to be neutral on hard news, while perhaps socially liberal on issues like gay rights or greater equality for ethnic minorities. Bill Maher and Jon Stewart are openly liberal cable TV hosts, while Glenn Beck (formerly of Fox, but now on his own TV channel) is conservative, as are all of the commentators on Fox and some on CNBC. You can decide who to watch.
Talk Radio
This is one media outlet where no one is scared to voice their opinion. Whether it be Conservative talk radio with Rush Limbaugh, Sean Hannity, Michael Savage, and Monica Crowley or Liberal talk radio with Ed Schultz, Stephanie Miller, Thom Hartmann, and Bill Press-- these personalities are generally without any nuance. They tend to be forceful, vocal, and ideological. They get straight to their point-- leaving no room for conciliatory comments from the opposition. While there are a few successful liberal talkers, it is worth noting that 95% of radio talk shows are hosted by right-wing conservatives.
Newspapers
In New York, for example, the New York Times' editorial board has a more liberal approach (although their news is generally neutral) while the Wall Street Journal's editorial page is generally conservative (and their news too is generally neutral); the entire New York Post is openly conservative, as is the Boston Herald. Most newspapers, however, are like USA Today-- they strive to be neutral and allow commentators from both sides. Consumers can choose which newspapers best suit their needs.
Magazines- find a niche
Like newspapers, magazines can be liberal, conservative, or totally neutral and focused on anything other than politics. Whatever your point of view, you can find a magazine to suit it-- liberals read The Nation, The Progressive, Mother Jones, and others; conservatives read the Weekly Standard, the American Thinker, and some who are more ultra-conservative read WorldNetDaily. News magazines like Time and The Week strive to be neutral.
Hollywood
One unarguable fact is that most Hollywood personalities are outspokenly in favor of liberal causes (Michael Moore, Leonardo DiCaprio, Alec Baldwin, etc...), although there are a few outspoken conservative personalities such as Jon Voight and Clint Eastwood.
Media Consolidation-- the real problem
Contrary to myth about the "liberal media"-- widely believed on the right, but totally untrue-- most media outlets are businesses, and they seek what will make money for their corporate shareholders. Thanks to media consolidation, a small number of large corporations dominate the media landscape, affecting what we see and how much it costs for us to see it. Both liberals and conservatives will continue to believe the other is in control, but the reality is that whatever will turn a profit rules. Thus, Fox News is profitable and very effective at promoting the views of conservatives and Republicans. MSNBC is not as monolithic, but its commentators do promote the views of liberals and progressives. While MSNBC's corporate parent leans conservative, the network is profitable so it will remain on the air as one of the few openly liberal networks as long as it continues to make money for Comcast, not because it is liberal.
