What to Read: Romance & Sex
There are so many great Christian resources on romance, desire, and sex, including both lay and scholarly commentaries on Song of Songs. Below some works/authors I highly recommend. You'll find them in the Calvary Church bookstore or online.
SONG OF SONGS
The best commentary for laypersons on the Song of Songs is Tom Gledhill's The Message of the Song of Songs. Any good study Bible will also provide some basic commentary.
For a scholarly treatment of the Song of Songs, look into works from Douglas Sean O'Donnel,Tremper Longman, Richard Hess, G. Lloyd Carr, and Marvin H. Pope. Pope's book is for specialists (pastors and scholars), but it is the best overall treatment of the history of the interpretation of the book.
INTIMACY & SEX
I recommend Laura Winner's book, Real Sex, for singles. It's hip, it's hot, and it takes a look at the issue reasonably.
Tommy Nelson's Book of Romance provides helpful advice for singles, although it is largely for married couples. My only caveat is that the commentary is incomplete.
Intended for Pleasure is a little outdated, but it is still a solid read for newlyweds and young couples. Dr. Ed and Gaye Wheat provide lots of very basic knowledge on human sexuality.
Intimacy Ignited is a reading of the Song of Songs for couples with helpful application on, as the title promises, igniting your sex life. The book is co-authored by two couples, Dr. Joseph & Linda Dillow and Dr. Peter & Lorraine Pintus.
Steve Gallagher's book, Out of the Depths of Sexual Sin, provides hope for people who are struggling with sexual addiction. The book contains a whole host of additional resources in this vein.