There are many excellent books to choose from; however, we recommend beginning with these:
  * The Essential Montessori, by Elizabeth Hainstock
  * Montessori and your child – A primer for parents, by Terry Mallory
  * The Secret of childhood, by Maria Montessori
  * Montessori – A Modern Approach, by Paula Polk Lillard
  * www.montessoriconnections.com 
  * www.michaelolaf.net

Additional Montessori reading can be found here