The WP says "Eighty percent of the traffic for news and information is vacuumed up by the top 7 percent of such sites, says an annual survey by the Project for Excellence in Journalism. These, according to Nielsen figures, are led by aggregator sites: Yahoo (No. 1, with 40.8 million unique monthly visitors), AOL (No. 3) and Google News (No. 6). The television news sites are also strong: MSNBC (2), CNN (4), Fox News (7) and ABC News (8). And three newspapers make the list: the New York Times (5), Washington Post (9) and USA Today (10, with 9.3 million unique visitors).
But all Web destinations are not created equal. Consumers spend more than twice as much time on cable TV sites (23 1/2 minutes a month) as on newspaper sites (10 minutes a month). Online-only sites fared only slightly better (12 1/2 minutes a month). Two political sites stand out: the right-leaning Drudge Report (nearly an hour each month) and the liberal Daily Kos (48 minutes). "
And the State of the News Media 2010 study has an excellent study of the relationship between bloggers and tweeters and the mainstream media sites they're referencing