From the US Department of Health and Human Services, this site offers a full suite of resources for understanding, coping with, and combating bullying and cyber-bullying for all ages. It includes risk factors, warning signs, and prevention strategies as well as tips for bystanders. This is the best first resource for those facing bullying.
From the American Psychological Association (APA) this page for students, teachers, and parents recommends best practices from psychologists for identifying and preventing bullying and cyber-bullying. The page includes sections for each group as well as a list of local resources and clinicians.
From the US Centers for Disease Control (CDC) this page summarizes the most credible resent research into bullying and youth violence and contains an extensive library of resources on sub-topics such as Electronic Aggression, Bullying and Suicide, and Sexual Bullying.