You might, for this exercise, quote heavily from Bias, by Bernard Goldburg. He did a radio interview with Rush Limbaugh recently, which you may be able to access if you or your dad is a 24/7 member.
I suggest, for brevity's sake, that you choose one topic on which to focus, and discuss media bias toward that one topic. For instance, Abortion and the Anti-War Movement have both been in the news lately; how have the major networks and press covered these hot topics? Or you could compare and contrast - Rush did some great coverage of the media's promotion of the war protests versus their lack of coverage of the Pro-Life Rally in Washington here. Here's another great analysis.
Focus your search on the Big Guns:
1. USA Today (Arlington, Va.) Circulation: 2,149,933
2. Wall Street Journal (New York, N.Y.) Circulation: 1,780,605
3. Times (New York, N.Y.) Circulation: 1,109,371
4. Times (Los Angeles) Circulation: 944,303
5. Post (Washington, D.C.) Circulation: 759,864
(For comparison here's the most widely read Conservative-leaning paper:
100. Times (Washington, D.C.) Circulation: 103,505)
Check out this info from The American Society of Newspaper Editors on their own findings of the American public's view of bias in the media:
78 percent of U.S. adults agree with the assessment that there is bias in the news media.
58 percent believe that the public's dissatisfaction with the media is justified - as opposed to 29 percent who say the press is "an easy target for deeper problems in our society."
78 percent believe that powerful people can get stories into the paper - or keep them out.
50 percent believe there are particular people or groups that get a "special break" in news coverage, and 45 percent believe that others "don't get a fair shake."
77 percent believe newspapers pay lots more attention to stories that support their own point of view.
Research stories by the "Big 3" as well, ABC, CBS, and NBC. They know their audience is declining, yet they persist in their biased attempts at journalism. Check out this quote from Ted Koppel: "In what may be one of the more tragic convergences in American history, public trust in reporters has reached an all-time low at precisely the time that the country is about to be inundated in information chaos. America may not want to believe it, but it has never had a greater need for its professional press corps. Reporters and news organizations may not want to hear it, but the country has never had a greater need for serious, no-nonsense reporting." This quote is from his foreword to the book, Live from the Trenches. Go here for review.
Also, get great info at RatherBiased on what Dan Rather gets away with.
I guess I've cited Rush quite a bit above, but perhaps that could be part of your argument as well, that Conservatives have few media outlets to turn to for news without a liberal bias, and Rush Limbaugh's popularity (2 million listerners) displays American's hunger for news without the liberal slant.
Obviously, that should read 20 million listeners.