A major archive for data on religion in the U.S. that incorporates a number of different datasets with information on religious groups, surveys of clergy, and data on denominations and congregations down to the county and city level in the U.S.
A study done every other year on social trends in the United States using a series of questions dealing with attitudes, behaviors, and demographics. Many of which are consistent year to year, allowing for tracking social trends over time.
The Kaiser Family Foundation (KFF) is a private non-profit organization that conducts research on issues related to U.S. healthcare and health policy. This portion of their site has data collected from KFF surveys.
The Pew Research Center collects a wide range of public opinion data on subjects like U.S. politics, media, social trends, religion, and technology. Many of their reports and datasets are available from their website.