Carol Benson and Allen Metz, Madonna Companion (1999)
One of the best Madonna books out there, this book compiles reviews, interviews, and academic papers on Madonna in a very broad and complete way.
Lucy O'Brien, Madonna: Like an Icon (2008)
Lucy O'Brien chronicles the career of Madonna.
Matthew Rettenmund, Encyclopedia Madonnica (1995)
It is what it sounds like, an encyclopedic reference books with everything from "academia" to "eyes."