I'm also an avid reader, and am disappointed with the comparative dearth of books for referees.
I've read three refereeing books so far.
One was "The Art of Refereeing" by Robert Evans and Edward Bellion. Absolutely fantastic book - it has elements of a refereeing manual, but also conveys the authors' whole philosophy of refereeing, along with plenty of autobiographical anecdotes. I would recommend it to every referee.
The other two were biographies - Pierluigi Collina's was ok, a pretty good read, and an interesting look inside the mind of the greatest referee of his time.
However, I much preferred Graham Poll's - much more interesting, much more in depth and personal, particularly about his struggles after the three yellow card incident, and a really good insight into the life of a top referee.
Now I just need to get my hands on David Elleray's and Jeff Winters, and look forward to any other recommendations here.