ADAA -- The Anxiety and Depression Association of America (ADAA) is a national nonprofit organization dedicated to the prevention and treatment of anxiety and depression and related disorders and to improving the lives of all people who suffer from them. Visit this comprehensive site for information about the treatment of anxiety as well as links lots of other resources.
National Institute of Mental Health -- The national clearinghouse for information about the number of people with anxiety and other mental illnesses, and information about the effectiveness of alternative therapies. Additionally, this site has links to clinical trials, some involving medicine and others that seek to find the genetic markers for anxiety in families with multiple people affected.
IOCDF -- The International Obsessive Compulsive Foundation has helpful resources for people with OCD as well as family and friends.