National Institutes of Health
National Institute of Mental Health: Bipolar Disorder
Very detailed description of bipolar disorder, its symptoms, diagnosis, and treatment. Includes information on how families and individuals can get help, and on the ways in which bipolar disorder affects children and adolescents.
The National Alliance on Mental Illness
National Alliance on Mental Illness: Depression
This site is a concise page from NAMI describing depression, its causes and symptoms, statistics, treatment, and more.