American Alliance of Museums
American Institute for Conservation
Association of Registrars and Collections Specialists
Canadian Conservation Institute
Conservation OnLine (CoOL)
Getty Conservation Institute
Northeast Documentation Conservation Center
Northern States Conservation Center
Packing, Art handling & Collections Care Information Network (PACCIN, a professional interest committee of the American Alliance of Museums)
Registrars Committee of the American Alliance of Museums
Western Museums Association


The Smithsonian Institution maintains a detailed (and very broadly defined) list of art conservation organizations. It can be found here: http://www.si.edu/mci/english/learn_more/taking_care/artorgs.html