The American Religious Tradition

"The book described nearly every denomination and the people who made them tick: Protestant groups from Anglican to Pentecostal, Catholicism, Judaism, Hinduism, Buddhism, neo-pagan groups and atheist associations, along with bibliographical references and mailing addresses.
'I quickly arranged to review it for a journal and then contacted Gordon, expecting to meet a frail guy of 80 who'd spent his entire life putting it together,' Stark said. 'Instead, he turned out to be this young Methodist preacher who'd done the whole thing in his attic.'"

Louis Sahagun in the Los Angeles Times profiles UC Santa Barbara's J. Gordon Melton, who wrote 1979's Encyclopedia of American Religions.

And by way of Ghost in the Machine, Regions of Mind weblog reprints maps depicting American religious identity, created by Glenmary Research Center.