The American Constitution Society
This organization states that it “promotes the vitality of the U.S. Constitution and the fundamental values it expresses: individual rights and liberties, genuine equality, access to justice, democracy and the rule of law.”
American Civil Liberties Union
This organization calls itself “our nation’s guardian of liberty.” It also states that it is “working daily in courts, legislatures and communities to defend and preserve the individual rights and liberties that the Constitution and laws of the United States guarantee everyone in this county.” You can find the website for the New York chapter here.
This organization calls itself “a group of conservatives and libertarians interested in the current state of the legal order.” It states “it is founded on the principles that the state exists to preserve freedom, that the separation of governmental powers is central to our Constitution, and that it is emphatically the province and duty of the judiciary to say what the law is, not what it should be.”