Below are some links of interest.
What is Barbershop? (the art of four part harmony)
Sweet Adelines International
Region 25 (home of Top of the Rock Chorus)
Region 25 Choruses | Region 25 Quartets
Other Regions (in the United States, Canada, Europe, Australia and New Zealand)
Pitch Pipe Magazine (official magazine of Sweet Adelines International)
Top of the Rock Chorus (Facebook) Facebook Logo
Top of the Rock Chorus (MySpace) MySpace Logo