Some pressure group resources

http://www.historylearningsite.co.uk/pressure_groups_in_america.htm

http://en.wikipedia.org/wiki/Politics_of_the_United_States#Political_pressure_groups

http://en.wikipedia.org/wiki/Advocacy_group

http://www.peterjepson.com/law/politics/US%20Pressure%20Groups.pdf

http://www.peterjepson.com/law/US-5%20Newman.pdf

http://www.twyman-whitney.com/americancitizen/links/lobbies.htm

http://tutor2u.net/blog/index.php/politics/C106/