Warning: for married men only.  This book was definitely on the more graphic side of Christian books on sex, though they're very open about it, at least the parts that talk about... mechanics. 

I thought this was a very well-done book, and wanted to go over a lot of it with my wife.

But considering this is a public website, I won't go into any more detail than that. I can't believe I actually included the book on the public list in the first place!