The first three titles on this list of examples were digitized by Google. Along with the Google Book project Google has also begun an effort to digitize backfiles of magazines. A list of what has been digitized has not been publicized but it does include The Bulletin of the Atomic Scientists, Life, Ebony, Jet, New York Magazine, Popular Mechanics, Popular Science and the NY tabloid, Weekly World News.
To find a topic or magazine, go the the Advanced Search option in Google Books.
1) Put in your search terms
2) Check the content box Magazines
3) If you are searching a specific title, put it in the dialog box labeled Book Title.
Below is a select list of freely available historic newspapers available on the web. For the library's holding of newspaper databases and news see the subtab Library Catalog-Primary Sources- Newspapers
To find additional freely available digitized historic newspapers see ICON: International Coalition on Newspapers. The ICON list describes and links to current newspaper digitization projects