Pew research center
The Pew Research Center is a nonpartisan "fact tank" that provides information on the issues, attitudes and trends shaping America and the world.
Religion
Association of Religion Data Archives (ARDA): data archive
The Association of Religion Data Archives (ARDA) strives to democratize access to the best data on religion. Founded as the American Religion Data Archive in 1997 and going online in 1998, the initial archive was targeted at researchers interested in American religion.
The religion and state project
Round 2 of the RAS dataset, which is currently the official version available for download, measures the extent of government involvement in religion (GIR) or the lack thereof for 1775 states on a yearly basis between 1990 and 2008.