The Hereditary Disease Foundation focuses on scientific issues related to genetic diseases, especially Huntington's. Their site is particularly informative about the ethical, legal, and social issues involved with testing for genetic diseases and provides good links to related Internet sites.
Huntington's Disease: Hope Through Research is a comprehensive booklet, available online from the National Institute of Neurological Disorders and Stroke (a member of the U.S. government National Institutes of Health), with information on diagnosis and presymptomatic testing, care, community resources, and research.
Huntington's Disease Society of America has a regularly updated site with extensive information about the disease, what's new in research, and where to find help, as well as a list of publications and videotapes available from the Society.