I heard a summary of this report on NPR. This is really interesting - you can search for numbers of people that affiliate with various denominations, or that are "unaffiliated". You can also look by map and in other ways. Check it out. However, be warned - the Pew survey seems to offer different numbers than some denominations currently advertise.
NPR emphasized that the study found that many Americans are NOT affiliated with the same religion of their parents, and that Americans tend to change their religious affiliation.