History

Ghosts of the Gridiron
Information on early professional teams in the Philadelphia area such as the Frankford Yellow Jackets, Pottsville Maroons and Philadelphia Quakers. Team histories, images, schedules, statistics, and period news articles.
http://www.geocities.com/ghostsofthegridiron/

The Helmet Project
Documents how the helmets for each team of the NFL, NCAA, NAIA, CIS, NFL Europe, Arena football, CFL, as well as defunct professional leagues, have changed over the years, as well as any interesting anecdotes about each.
http://www.nationalchamps.net/Helmet_Project/

Leather Helmet Illustrated
Monthly magazine about the history and traditions of college and professional football, from the early days to the present.
http://www.leatherhelmetillus.com

Professional Football Researchers Association (PFRA)
History of professional football, including the players, teams, leagues, games and stories from the National Football League (NFL), World Football League (WFL), United States Football League (USFL) and other professional leagues.
http://www.footballresearch.org/