http://www.anred.com
http://www.somethingfishy.org
Both are excellent self-help web sites for eating disorders, including definitions, warning signs, statistics, self-help advice, etc. ANRED (Anorexia Nervosa and Related Eating Disorders) also has good information on over-exercise disorders. ANRED is a bit more educationally focused. Somethingfishy offers interactive chat forums and inspirational stories in addition to its educational/diagnostic pieces.
http://www.nationaleatingdisorders.org
This web site addresses body image, how to help a friend, parent concerns, and further resources.
http://www.closetoyou.org/eatingdisorders/
The information given here includes medical information, what eating disorders are, steps to recovery and finding treatment, as well as poems/stories and other reading material on the subject.

