Written by the co-founder of BeliefNet.com, Steven Waldman, this book sounds interesting:
Founding Faith: Providence, Politics, and the Birth of Religious Freedom in America
I found out about it from his interview with Terri Gross on NPR's Fresh Air. You can find an exerpt from the book here also.
I plan to read it after I finish this engaging book:
Evolution for Everyone: How Darwin's Theory Can Change the Way We Think About Our Lives