Americans United for Separation of Church and State is a nonpartisan educational organization dedicated to preserving the constitutional principle of church-state separation as the only way to ensure religious freedom for all Americans. They are active in the courts, in lobbying lawmakers at the national and state levels, and in the arena of public opinion. Donate here.
The Freedom From Religion Foundation promotes the constitutional principle of separation of state and church and educates the public on matters relating to nontheism. The group is active in the courts and in the arena of public opinion. Donate here.
The American Civil Liberties Union is active in promoting both the free exercise of religion and the separation of church and state. They are active in the courts, in lobbying lawmakers and the federal and state levels, and in the arena of public opinion. Find out about their efforts to protect religious liberty or donate here. Note that the ACLU is involved in numerous causes and this donation page does not allow you to indicate which of their many excellent causes you are supporting.