PigskinHeaven.com [more]
NFL, College, and fantasy football forums.
http://www.pigskinheaven.com/

Quarterback Passer Rating Calculator [more]
Rates quarterbacks by attempts, completions, passing yards, touchdowns, and interceptions. NFL, NCAA, and Arena Football League calculations available.
http://www.primecomputing.com/

SearchQB.com [more]
Customized search engine focused on football.
http://www.searchqb.com

Wikipedia: American football [more]
Encyclopedia article covering the history of the sport, its popularity, rules, basic strategy, and physicality.
http://en.wikipedia.org/wiki/American_football