This book by Eric and Leslie Ludy (mostly Eric) was NOT what I expected when I picked it up as a newlywed, but it is hands down the best book I can recommend on sex to young, unmarried folks. Eric treats the subject with delicacy, never stepping outside the realm of what would be appropriate. The book itself is written as a story about Eric himself, when he decides to try to have an interview with Great Sex or "Mr. Smith." In order to earn the rare priveledge, he must go through Mr Smith's four bodyguards--the first of which is Purity. At the end of the book, after finally earning the privileged interview, Eric, along with the reader, makes a surprising discovery.
When I say this is good for "young folks" I do mean pretty young, I think this book is appropriate in the teen years at the point which the young person begins to experience pressure in the sexual arena (whether outside pressure from peers, or inward pressure from self). Obviously, this age will vary with each individual. This book is NOT about details, instead Eric focuses on having a Godly, Biblical perspective on the topic, particularly focusing on those in their single years.
At the end of the book Leslie has a chapter that deals with some "FAQs" that young people have on the topic. This chapter (which is outside of the story portion that takes up most of the book) is the only portion of the book that goes into detail, but Leslie does so in a godly reserved way, keeping the veil drawn over the bedroom. The book can be useful with or without this section, though if parents prefer not to have their teens read this part they should consider answering the FAQs themselves. There is a reason the questions are "frequently asked." :-)