The many school shootings of the past two years have taught us to pay attention to obvious red flags like your son's kill list. I do not encourage parents to spy on their kids or to search their rooms but in this case I would suggest that you search your son's room and your entire house for any firearms, weapons or bomb-making apparatus.
You must also seek immediate psychological counseling for your son as well as alert your son's school authorities. This must be regarded as an emergency situation. In the wake of the Littleton killings, be prepared for the school administration to suspend your child until mental health professionals deem him not to be a threat to others and to himself.
Your son desperately needs intensive professional help and support. Even if this list is merely a fantasy management of his anger, disappointment, isolation and hurt, he is a very sad, troubled boy who is crying out for help. Well, you have fortunately heard his cry and you will get him the help that he needs. I know that you are probably in a very confused state of panic at this time. Please know that your intervention is needed now. Get some help and support for yourself. Don't try to tough this out alone. Your son's list does not mean that you have failed him as a parent. It means that he has become hopeless in the face of inner torment and that he has not been able to reveal his pain to you or anyone. Now you know his pain. Now he can begin to be healed. I'll keep a good thought for you and your boy. Write me if I may be of any further help or support.