I found a really good Yahoo! group discussing the dangers of vaccinations for dogs and cats. It's a very active forum with over 1900 members. You have to join the forum though, even just to read the posts. Here's a brief description of the forum:
This list is intended for those who are interested in discovering the truth about the dangers vaccines, drugs and pesticides, pose to the animals in their care. This list is also structured for those who are adamantly opposed to vaccinations. Alternatives to vaccines, such as improved species appropriate diet, homeopathy, and various holistic methods of care, are topics of discussion as well. Problems with other allopathic (mainstream) drugs will be discussed, including heartworm drugs, arthritis drugs, and others.
http://pets.groups.yahoo.com/group/jstsayno2vaccs/