Listmania!
Marriage - Sex
By an Amazon.com customer
A Celebration of Sex: A Guide to Enjoying God's Gift of Sexual IntimacyA Celebration of Sex: A Guide to Enjoying God's Gift of Sexual Intimacy by Douglas E. Rosenau
Buy new: $12.23 / Used from: $8.82
The single best text on sex in marriage ever written.  If you can only buy one book on the subject.  This is the one to buy.
A Celebration of Sex After 50A Celebration of Sex After 50 by Dr. Douglas E. Rosenau
Buy new: $12.34 / Used from: $4.94
A good supplement to the original; however, I recommend getting both.
A Celebration of Sex for NewlywedsA Celebration of Sex for Newlyweds by Dr. Douglas E. Rosenau
Buy new: $9.99 / Used from: $4.87
A good engagement gift for the Christian couple.  Pair it with the original.