Christopher Alexander has finished the fourth book in his series, The Nature of Order. More on this later. In the meantime, there's a nice interview with him on NPR, available here.
NB: Alexander has his own website, about the only place you can find a coherent list of his books. The titles of the four books in The Nature of Order are:
The Phenomenon of Life
The Process of Creating Life
A Vision of a Living World (3rd in series, most recent publication)
The Luminous Ground