I found a great article on World Religions by Adherents.com. Adherents.com is a growing collection of over 43,870 adherent statistics and religious geography citations: references to published membership/adherent statistics and congregation statistics for over 4,200 religions, churches, denominations, religious bodies, faith groups, tribes, cultures, movements, ultimate concerns, etc. The religions of the world are enumerated here.
Basically, researchers can use this site to answer such questions as "How many Lutherans live in Wisconsin?", "What are the major religions of India?", or "What percentage of the world is Muslim?" We present data from both primary research sources such as government census reports, statistical sampling surveys and organizational reporting, as well as citations from secondary literature which mention adherent statistics.