I would like to highlight an organization that works to combat censorship for the visual arts. The National Coalition Against Censorship has many different programs dedicated to protecting free expression including a project specific to visual arts advocacy.
The NCAC website has many resources including an ‘art law library’ and a news page. The work that they do (an example can be seen in this letter protesting the removal of a painting from an exhibition because it depicted a *gasp* nude figure) is critical to maintaining freedom of expression and inquiry.
The NCAC is also involved with the File Room project by artist Antonio Muntadas.