Bias comes in many forms, from the outright advocacy Driscoll mentions to simply not covering stories that shine a poor light on the cause. Most conservatives are convinced of this, however many on the left disagree and say there is no media bias whatsoever aside from Fox News.
So here's something from the MRC archives on media bias circa 2005, taken from a University of Connecticut Department of Public Policy survey of 300 print and TV media figures on a variety of topics. Not only did it confirm that a large majority voted for Kerry over Bush, it also contained this nugget:
When asked about the Bill of Rights, nearly all journalists deemed “essential” the right of a fair trial (97%), a free press (96%), freedom of religion (95%) and free speech (92%), and 80 percent called “essential” the judicially-derived “right to privacy.” But only 25 percent of the journalists termed the “right to own firearms” essential, while 42 percent called that right “important but not essential,” and 31 percent of journalists rejected the Second Amendment as “not important.”Bold added to confirm that our advocacy media is just continuing to do what they do best.