I added some links to the "Resources" sidebar:
The Artists Foundation is based in Boston, but it has practical information for all artists on such topics as writing a resume or grant application, and information on copyrights, studio spaces and gallery relations.
Edward Winkleman offers the best advice on getting a gallery I ever came across; and it's written by an experienced art dealer, and one of the best art bloggers out there.
The Foundation Center is an enormous (too big) resource for grants. It has everything!
New York Artists Equity is a way to get group health insurance and other services.
Volunteer Lawyers for the Arts provides legal services to artists and information about such things as intellectual property rights and contracts with galleries.
Please comment if you have other suggestions.