Known more familiarly as the AKC; probably the most well-known kennel club. It has not always been "pit bull friendly"; however, it does recognize the breed under the name American Staffordshire Terrier. It enforces strict requirements and standards in order to promote the integrity of the breeds it recognizes. A very informative website with plenty of breed information and links to other clubs and organizations.
The UKC is the other of the "Big Two" kennel clubs. It was the first kennel club to officially recognize the American Pit Bull Terrier and has a strict policy against associating itself with any organization which sanctions dog-fighting. Like the AKC, it has rigid standards. Registration without a three-generation pedigree is difficult. Its website is also very informative and a good source of breed information.
Founded in 1909, the ADBA is a registry devoted exclusively to the American Pit Bull Terrier. While it does not deny the fighting history of the pit bulldog, it strives to promote responsible ownership of the APBT, and officially decries all illegal activities involving the breed. The organization actively strives to dispel the myths and misunderstandings of this wonderful breed, as well as provides support to the Endangered Breeds Association, a group which opposes anti-Pit Bull legislation.
The Continental Kennel Club is easier to register with if you do not have a three-generation pedigree, and is a place to start if you are founding your own bloodline but do not have a pedigree started. It is an all-breed club, recognizing some breeds not acknowledged by other kennel clubs. It also registers some popular hybrids, such as the Pekapoo, with an eye on developing new breeds. Color photo registrations are available, as well as pedigree services, DNA certification, and microchip IDs.