Census data

historical data from the US Census of population and housing is available at http://www.census.gov/prod/www/abs/decennial/index.html (1790-2000)

old magazines

Google books has older magazines like Life fully scanned, available, and free (at least for now) See: http://books.google.com/books or http://books.google.com/books?id=s1QEAAAAMBAJ&source=gbs_slider_gbs_user_shelves_1004_homepage