"Algebra in the Early Grades"

This book was published in 2007, but is one of the most interesting new books in mathematics education. The book is edited by James J. Kaput, David W. Carraher and Maria L. Blanton, and it offers a "comprehensive, research based, multi-faceted look at issues in early algebra" (according to the description provided by Google Books). Also check out the description in the NCTM product catalog!