My book list also includes:
Slightly less technical than the Walsh book, but updated in 2010, is "Dr. Peter Scardino's Prostate Book" (2nd edition).
I've read both, and find Scardino's book a good alternative. In the new edition there are more useful diagrams, and some areas that I though were vague in the older edition are improved. Also, being a 2010 edition, some of the factual details are more up to date.
Walsh is more brutally clear on some points.