Mixed Breed Dog Clubs of America
A national registry for mixed breeds, providing many of the same opportunities that the American Kennel Club (AKC) offers for purebreds.
http://www.mbdca.org/

Dog Registry of America, Inc.
Open to all breeds of dogs. They register over 300 breeds of dogs and breeds unrecognized by other kennel clubs. You can register your dog or kennel online.
http://www.dogpapers.com/

American Dog Owners Association
Since 1970 has been promoting, protecting and defending responsible dog ownership. Information on past and pending dog legislation, list of pet owner's rights, and a printable membership application.
http://www.adoa.org/

Canadian Rarities
Ancient and rare dog breed club. Lists shows in USA and Canada, and different titles for your dog to win.
http://www.vaxxine.com/rarities

K9Z
A club for owners and fans of crossbreeds and mongrels. Offering picture competitions, shows, games, and membership information.
http://web.ukonline.co.uk/k9z.uk/

American Canine Association
An all-breed, international canine registry. Established its own conformation titles, obedience titles and also recognizes lineage and titles established and obtained by, and from, other registries and breed clubs.
http://www.acacanines.com