Due to the Sonny Bono copyright act of 1998, everything produced since 1922 is under copyright protection, which means it's prohibitively expensive for most libraries to acquire searchable databases of newspapers of that era.
The law created a problem for anyone doing newspaper research after 1923, thus there are few websites for digitized newspapers. At two sites, news.google.com/newspapers and newspaperarchive.com selections seem random and incomplete.
Newspapers Online, http://www.newspapers.com has links to tons of newspapers as well as trade, religious, specialty and business publications. It also links to state press associations and college newspapers. Although it does not provide a complete list, its low-graphic content and wide-ranging offerings make it a very effective search site. Has email addresses and URLs.
The American Journalism Review site, http://www.newslink.org. Also has a large number of geographically organized newspapers, both within and outside of the United States, but also lists and links to the 50 largest circulation magazines in the states and the 25 largest circulation magazines in Canada. Not every large circulation magazine has a link because many do not have web pages.
A linked index of more than 3,500 newspapers,http://www.all-links.com/newscentral. Some links are dead.
One site that crosses the bridge between searches for publications and searches for stories is My Virtual A nearly comprehensive listing of links to online newspapers, E-zines and sources, http://www.kirklapointe.com/world.html.
UNZI.org is a fabulous free website to locate Periodicals, Books, and Videos, www.unz.org!