About.com: Football History: Includes annual award winners, Super Bowl and NFL Draft History plus franchise genealogy.
Chris Creamer's SportsLogos.net: History of the logos of the National Football League, part of a virtual museum of sports logos and uniforms.
Chronological History of the Modern NFL: A time line of how the NFL grew from 1933 - 2001.
Football @ JT-SW.com: Database of NFL history with team and player statistics from 1920 to present day, including some box scores.
Football Junk: NFL Statistics for each player, team, and league in pro football history.
Football.com - NFL History: Genealogy, current teams and defunct franchises.
Ghosts of the Gridiron: The Early Days of Pro Football in the Philadelphia Area.
Golden Age Era Sports: Football: A history of the leagues and teams from the Golden Age of Radio (1920-1967).
HickockSports.com: List of passing, rushing, receiving, scoring, interception, punting and punt return leaders.
I-NFL Helmet: Offers the history of each NFL team's helmet logo.
Infoplease: Football Almanac: Database including Super Bowl statistics, leaders, champions and awards dating back to 1920.
NFL History: Capsule histories of every NFL team.
NFL Legends: Capsule histories of legendary players and teams.
NFL Team Nicknames:
NFL.com: History: Franchise history, nicknames, draft history and famous dates.
Orange Athletic Club of New Jersey: Complete Football Records (1887-1936)
Pro Football Hall of Fame: History: Chronology, events, champions, former players, draft history and team information.
Pro Football Reference: A database containing historial stats from every NFL team and most of the players.
Professional Foortball Researchers Association in Western NY: Articles on professional football in Western NY prior to 1970.
The American Football League (1960-1969): Offers history, facts, photos, cards and player information.
The NFL History Network: A fan-operated site with individual team histories, statistics, box scores and trivia.
Wikipedia: Defunct NFL Teams: Encyclopedia article on teams no longer in existence.