The ARBA - American Rabbit Breeders Association
site is here
This club is for all breeds. The ARBA is the main club/organization. All the other clubs usually follow their rules, and endorse their breeds. The ARBA has many recognized breeds. A breed can only be shown at ARBA shows if it is recognized. The ARBA also has having a book that is published every three years and stating what the perfect rabbit of each breed (that the ARBA recognizes), is supposed to look like. When you join, you get 6 issues per year of Domestic Rabbits magazine, as well as a guidebook written by the ARBA.
The WSHLRC -Washington State Holland Lop Rabbit Club
site is here
This club is really only useful if you live in WA state or attend many WA shows. Membership fee is very cheap (only $5 for youth, $7 for an adult), and when you join, you get a discount off the fee that is charged per rabbit when you enter in a show.
The HLRSC - Holland Lop Rabbit Specialty Club
site is here
This club is very helpful. When you join you get an official guidebook, 4 issues of The Hollander, a magazine exploring several different aspects of raising rabbits with articles by various authors.
There are many other rabbit clubs for many other breeds. These are only a few.