Bishop John Shelby Spong, Living in Sin: A Bishop Rethinks Human Sexuality, 1988.
I can't remember if I looked at this book before, or not. Reading it, it seems to me to be far from controversial, far from overly challening. In fact, seventeen or so years after it was published, it almost reflects the status quo--or will, as soon as we start blessing same-sex marriages in the Anglican church. In short, while it reflects on an argument, and was at the time of its publication quite challenging, the book is more saddening than anything else--saddening that, as a church, we've made so little progress in almost twenty years.
Spong zips along through a history of marriage in the church, carefully goes through the biblical arguments about sexuality (and goes through the two major approaches to sexuality), and then makes three proposals: institute "betrothal", or a recognition of a meaningful relationship between two people that occurs prior to marriage but that can include a sexual component; allow the blessing of same-sex unions; and recognise that post-married people still are sexual beings, and that we shouldn't limit their options, either.
Throughout the book, he stays within one view that he's always maintained: sex can exist in both good and bad forms in human life, and that it's the church's job to celebrate what is good and work against that which is destructive and dangerous. It's not a riveting book; nowadays, just reading the Statement of Koinonia covers the basic outlines of his argument. It does, however, provide a decent introduction to a subject that still seems to have far too much of the church's attention.