Several groups have legal forms, pamphlets and workbooks on writing a living will, selecting a health care agent, and starting conversations with your family and doctors about your wishes should you become incapacitated.
Caring Conversations is a workbook published by the Center for Practical Bioethics. It includes a guide to difficult conversations with family about end-of-life issues, as well as advance directive documents and forms for designating someone as your healthcare agent.
Consumer's Toolkit for Healthcare Advance Planning from the American Bar Association is a highly detailed workbook that helps you identify a good healthcare agent, check that they understand your values, and specify some of the medical conditions and treatments that most worry you.
Making Health Care Decision for Others from Montefiore Medical Center offers valuable advice to healthcare agents or surrogates, helping them understand what it means to make decisions for others in dire situations.
Five Wishes from Aging with Dignity combines an easy-to-understand living will form with a form for designating a healthcare agent.
Growth House is a comprehensive web site that offers reliable information on just about any issue related to end-of-life care. The "Handbook for Mortals" and "Death with Dignity" sections contain details about dealing with pain, use of feeding tubes, and various kinds of advanced directives.