AAM: American Alliance of Museums has been a leader in developing best practices and advocating for museums, as well as providing a host of opportunities to museum staff and volunteers. Membership is reasonably priced -- if you're inclined to join -- and provides many benefits, including access to its Resource Library and the full archive of its flagship publication, Museum Magazine. In addition to a topics page, blog postings, data and fact sheets, the site also links to Museopunks, a podcast on progressive museum work.
ICOM [International Council of Museums] housed at the UNESCO building in Paris, is an international organization representing museums and museum professionals. Founded in 1946, ICOM represents 136 countries and territories. In addition to publishing standards, ethical guidelines, issue statements, bibliographies, and Red Lists (of threatened cultural properties across the globe), it also provides substantial news content.
The Official Museum Directory (Access provided via Harvard) is the authority for reliable museum data. The Directory is a one-stop source for museum professionals, students, library patrons, and researchers who need comprehensive information on those institutions committed to celebrating and preserving the world’s culture, art, music, nature, and history.