Up next on my list:
Language Evolution: Contact, Competition and Change, by Salikoko S. Mufwene. I met Professor Mufwene briefly when I was a graduate student at the University of Chicago and he was chairman of its linguistics department. He is a very impressive person. I look forward to reading his book, especially since "invisible hand" is one of its central organizing concepts, and appears already on p. 2 and throughout the book.