A brief search on amazon.co.uk brought up the following reference works relating the Turing's life, work and legacy.
I have ommitted works of fiction and some print-on-demand titles. I have tried to give some annotation although I only know a few of these books at all well. Where possible I have provided a link to a book review. Clicking on the titles will take you to the amazon.co.uk listing for further bibliographic information, 'Look Inside' etc.
B. Jack Copeland (ed.), The Essential Turing, Oxford University Press, 2004.
Turing's outut, each item being comprehensively summarised and explained. Review
Andrew Hodges, Turing (Great Philosophers), Routledge, 1999. From the back cover: "...critical analysis of Turing's developing thought, relating to his extraordinary life, and also to more recent ideas of Roger Penrose."
Christof Teuscher (ed.), Alan Turing: Life and Legacy of a Great Thinker, Springer, Berlin, 2004.
Beautifully produced but loosely edited conference proceedings: high quality articles aimed at a professional readership. Bonuses: foreword by Douglas Hofstadter and a translation of Valeria Patera's play Adam's Apple: Hacking the Turing Test.
Sara Turing, Alan M. Turing: Centenary Edition, Cambridge University Press, 2012.
The 1959 Biography of Turing by his mother, this edition having a new foreword by Martin Davis and an afterword by Turing's brother.