America's newspaper industry trade association provides a fantastic resource for quantitiative data on the news industry going back more than 50 years. This is the place to start if you need information on circulation, advertising expenditures, revenues, etc.
This is a terrific site about the American newspaper and the manner in which it has reported historical events. It is a useful both for the study of history, and the exploration of history as it has been recorded by newspapers. It provides reference materials, primary sources, digital images of newspaper editions covering historic events and brief essays on various topics such as newspaper technology and women journalists. There is even a section on the great hoaxes in journalism history.
This site provides a useful research guide to the study of American female journalists. A bibliography of recommended reading and links to primary sources are included.
This site provides a useful journalism history timeline as well as some interesting "FAQs" about American journalism.