One of the best resources I have found on the origins of the Rosary is the book Beads & Prayers: The Rosary in History and Devotions by John D. Miller. Not only does the book include a wonderful chronology of its evolution, it also goes into great depth on the meaning and spiritual significance of what is known today as the Dominican Rosary.
The book is filled with a wealth of historical information, but it does not read like a stale listing of dates and events. Rather, the author guides the reader in with his devout understanding of the Christian faith and the significance of Mary, the Mother of God, in biblical accounts and traditions of Christianity.
As a convert to Catholicism from the Lutheran Church, understanding the role of Mary in the Catholic Church was a struggle for me. This book was very instrumental in my quest for answers and ultimate acceptance of giving Mary a special place in my own journey of faith.