GoldwatersGhost

The International Society for Individual Liberty is an association of individuals and organizations dedicated to building a free and peaceful world, respect for individual rights and liberties, and an open and competitive economic system based on voluntary exchange and free trade. ISIL is a non-partisan educational foundation which is dedicated to building a worldwide grassroots movement for liberty.
http://www.isil.org

Electronic Freedom Foundation
Long before I became politically aware I admired the EFF for the defense of free speech online. Today they are the premiere organization fighting for liberty on the digital front. By blending the expertise of lawyers, policy analysts, activists, and technologists, EFF achieves significant victories on behalf of consumers and the general public. EFF fights for freedom primarily in the courts, bringing and defending lawsuits even when that means taking on the US government or large corporations.
http://www.eff.org

The Free State Project
The Free State Project is an agreement among 20,000 pro-liberty activists to move to New Hampshire, where they will exert the fullest practical effort toward the creation of a society in which the maximum role of government is the protection of life, liberty, and property. While I don't plan to pack up quite yet, this movement could set a mighty president of how successful a liberty enhanced society can be.
http://www.freestateproject.org

CATO Institute
The Cato Institute seeks to engage people in questions of public policy and the proper role of government. This is hands-down one of the best public policy institutes for informative, smart, political research, even if you hold a healthy skepticism of think-groups. A few hours browsing through the wealth of articles at Cato is a testament to many constitutional reinforcing goals and a very different idea about the right stands for.
http://www.cato.org

The Goldwater Institute
This one was bound to make the list...In keeping with the principles advanced by Senator Barry Goldwater, the Goldwater Institute is dedicated to protecting and expanding economic freedom, constitutional liberty and educational opportunity. The Goldwater Institute meets public policy challenges with innovative solutions that maximize our freedoms and keep government within its constitutional boundaries.
http://www.goldwaterinstitute.org

Foundation for Economic Education
The FEE is one of the oldest free-market organizations in the United States. Founded in 1946 by Leonard E. Read to study and advance the freedom philosophy. FEE's mission is to offer the most consistent case for the "first principles" of freedom: the sanctity of private property, the rule of law, the free market, and the moral superiority of individual choice and responsibility over coercion.
http://www.fee.org

The John Birch Society
Simply put, The purpose of the JBS is to bring about less government, more responsibility, and a better world by providing leadership, education, and organized volunteer action in accordance with Constitutional principles. The John Birch Society has been consistently dedicated to restoring and preserving freedom under the United States Constitution.
http://www.jbs.org

Association of Libertarian Feminists
The purpose of the ALF is to encourage women to become economically self-sufficient and psychologically independent. To publicize and promote realistic attitudes toward female competence, achievement, and potential. The opposition of the abridgment of individual rights by any government on account of sex. To work toward changing sexist attitudes and behavior exhibited by individuals. The movement prides itself on providing a libertarian alternative to those aspects of the women s movement that tend to discourage independence and individuality
http://www.alf.org

The Center For Small Government
The Center For Small Government is a non-partisan, grass roots organization with thousands of generous and enthusiastic volunteers and donors. Their efforts put an End the Income Tax in Massachusetts initiative on the ballot in 2002. It won an unprecedented 45% of the vote - in a state that's a hotbed of Big Government.
http://www.centerforsmallgovernment.com

The Reason Foundation
Reason advances a free society by developing, applying, and promoting libertarian principles, including individual liberty, free markets, and the rule of law. The foundation's nonpartisan public policy research promotes choice, competition, and a dynamic market economy as the foundation for human dignity and progress.
http://www.reason.org