Self-Guided Tour Organizers
Bike Tours Direct   Worldwide
Breton Bikes (France)
Cycling Sideways (Wales)
Discover France (France)
Diverse Directions (France, Vermont)
Freewheeling Tours (Worldwide)
Independent Cycle Tours (New Zealand)
Irish Cycling Tours (Ireland)
Iron Donkey (Ireland, England, Wales, Italy)
LoireLife Cycling (Loire Valley, France)
Natures Highway (New Zealand)
Pure-Adventures (Europe)
Randonnee Tours  (Canada, France, Ireland, Italy, Spain, U.S.)
Top Bicycle Tours (Europe, Eastern Europe)
Tulip Cycling (Holland)

Group Self-Guided Tour Organizers
Bicycle Adventure Club (Worldwide)
Bike and the Like Tours (New England, California)
Cycling Poland (Poland) 
Organized Touring Resources
Adventure Cycling Association
This is a great organization, leading the way in the development of bicycle routes across the country. Their maps are prized among tourists as the best and most complete in the country. Their site is a great resource on bicycle touring, and their data base of tour organizers lets you search hundreds of tour organizers by destination and the type of touring you want to do. If you're interested in bike touring, this is an organization worth joining.