These are good sources for learning about upcoming tournaments, staying in touch with the current events in badminton, learning the rules, purchasing videos of recent tournaments, and getting tips on how to play:

Upcoming and recent event in the Mid-Atlantic states: http://www.geocities.com/mida_shuttlecocks/

The United States Badminton Association:
http://www.usabadminton.org/

The International Badminton Federation:
http://www.intbadfed.org/