NAMI (National Alliance on Mental Health) there is a plethora of information on almost any mental health topic
Depression and Bipolar Support Alliance Locate an in-person or online group
The Schizophrenia and Related Disorders Alliance of America facilitates groups nationwide; find one on its site
Eating Disorder Hope catalogs online support groups
DailyStrength hosts a web forum where people dealing with self-injury can find encouragement, understanding, and a new way to cope
After Silence is a message board and chat room for victims of sexual violence.
The Postpartum Progress site lists support groups in nearly every state as well as in Canada and maintains an online forum.