Therefore keep watch, because you do not know the day or the hour. Matthew 25:13 (NIV)
These are organizations that are active in defending Christians and Christian interests on the legal front. Although not all are purely Christian in the cases they take, they are fighting the good fight and your donations would be money well spent.
Alliance Defending Freedom. An alliance-building legal organization that advocates for the right of people to freely live out their faith.
The American Center for Law and Justice. Headed by Jay Sekulow, the ACLJ is an explicitly Christian organization. Jay often appears on TV defending religious liberty.
The Beckett Fund is devoted specifically to defending religious liberty.
Foundation for Individual Rights in Education (FIRE). From their website: The mission of FIRE is to defend and sustain individual rights at America’s colleges and universities. These rights include freedom of speech, legal equality, due process, religious liberty, and sanctity of conscience.
Judicial Watch. Dedicated to government transparency and Constitutional principles, Judicial Watch is involved in much more than religious issues, but has been prominent in a number of religious liberty cases. Lots of info above and beyond court cases.
Liberty Counsel. From their website: they are an international nonprofit litigation, education, and policy organization dedicated to advancing religious freedom, the sanctity of life, and the family since 1989, by providing pro bono assistance and representation on these and related topics.