• Association of Children's Museums
• The National Center for Preservation Technology and Training - Resources
• VSA Arts - an international, nonprofit organization dedicated to promoting artistic excellence and providing educational opportunities through the arts for children and adults with disabilities. 

Support

• The Foundation Center
• Institute of Museum and Library Services (IMLS)
• The National Endowment for the Humanities
• Shaping Outcomes
• National Endowment for the Arts

Heritage Web Sites

• Heritage Preservation Links

National Associations

• American Association of Museums
  Broad organization for professionals in museums and museum related fields.  Has a bookstore.  Annual Conference.
• American Association of State and Local History
• Arts Reach
• Association for Preservation Technology International
• Association of Art Museum Directors (AAMD)
• Association of Science-Technology Centers (ASTC)
  This association represents over 400 science and technology museums, and hosts an annual conference.
• International Council of Museums (ICOM)
• National Association of Interpretation (NAI)
  Link for those involved in cultural, historical, and natural interpretation.  Conferences.
• National Endowment for the Arts
• National Endowment for the Humanities
• National Trust for Historic Preservation
• National Park Service
• Museum Store Association (MSA)
• Organization of American Historians

Regional Associations

• Association of Midwest Museums
• Mid-Atlantic Association of Museums (MAAM)
• Mountain-Plains Association of Museums
• New England Museum Association
• Western Museum Association

State Associations

• Alabama Museums Association
• Arkansas Museum Association
• Florida Association of Museums
• Georgia Association of Museums and Galleries
• Louisiana Association of Museums
• Mississippi Museums Association 
• North Carolina Museums Council
• South Carolina Federation of Museums
• Tennessee Association of Museums
• Texas Association of Museums
• Virginia Association of Museums
• West Virginia Association of Museums

Jobs

• ArtHire
• ASTC Job Bank
• Canadian Museum Network & Canadian Heritage Information Network - job postings
• The Chronicle of Philanthropy - Job openings in the non-profit world
• FedWorld - US Government federal job search
• Museum Job Resources On-Line
• Non Profit Career Network
• Washington Post - Jobs