The Complete Guide to Chirstian Denominations by Ron Rhodes

The Complete Guide to Christian Denominations by Ron Rhodes -- 440 pages
One Christ, Many Creeds by Erik Rottmann -- 95 pages

I read both of these books for a class.  Both were very interesting to read.
One Christ, Many Creeds gave brief overviews of the theologies of sixteen major Christian denominations in America.
The Complete Guide to Christian Denominations gave a more in-depth history and theology of the major denominations as well as the smaller groups that make up those denominations.
I would recommend both books to those interested in Christianity and its history in America -- especially the Complete Guide.