International Sailing Federation (ISAF) - the governing body for the sport of sailing.
International Dragon Association (IDA) - Info on rules & regulations, good listing of boats for sale as well as boatbuilders, sailmakers etc. They also have a good forum for discussion about Dragons and sailing.
National Dragon Associations
Australian Dragon Association - lots of good information from another association with a large geography and a concentrated urban population - they have been successful in building up their numbers recently.
British Dragon Association - has good listings of boats/gear for sale/wanted as well as information on Classic Dragons.
French Dragon Association
Cannes Dragon International
Complete list of National Dragon Associations from the IDA
British Dragons Annual Yearbook
German/Swiss/Austrian/Hungarian Annual Magazine