The Lewy Body Dementia Association provides general information about the disease, support information for caregivers, a newsletter, and lots of links.
Hosted by the University of Nottingham (UK), LewyNet provides a lot of information without too much obtuse medical jargon.
Technical Articles/Current Research
A great source of information is the National Library of Medicine. Enter "Lewy body disease" into the search field to find abstracts of published research articles.
The Alzheimer's Association has several message boards, including one for caregivers and another for getting advice from care consultants (not specific to Lewy body disease).