History of religious liberty

Supreme Court
Torcaso v. Watkins, 367 US 488 (1961)
United States v. Seeger, 380 US 163 (1965)
Employment Division v. Smith, 485 US 660 (1988)

Some major church-state cases

'Play in the joints' in the religion clauses, by William K. Norton
Gaustad, Edwin, Church and State in America, Religion in American Public Life Series: Oxford University Press (1999)
A Teacher's Guide to Religion in Public Schools
A Parent's Guide to Religion in the Public Schools
Religion in American History: What to Teach and How
Religious Expression in Public Schools: A Statement of Principles