For couples that are engaged, they can try 'Preparing for Marriage: Discover God's Plan for a Lifetime of Love' by Dennis Rainey. '10 Great Dates before You Say "I Do"' by Claudia Arp is great too. These books consider modern life and provide a guidebook of sorts for what to expect in a marriage. Books by Gary Chapman are a gem, and very popular amongst the Christian community.
My husband and I are reading 'Strengthening Your Marriage' by Wayne A. Mack. It's quite a useful guide for defining what a Christian marriage is all about, and what the roles of a husband and wife are. Although I do find the book quite outdated in terms of its ideas (it was written in the 1970s after all), I would say that it is quite a balanced book, and does give good advice and tips on how to make your marriage strong. But of course, it's important to put what you learnt in practice!
There are some wonderful books out there that provide insight about marriage from a Christian perspective. These books, when coupled with marriage counseling and other forms of meaningful dialogue, can sustain and growth the marriage bond. Great examples of books include: Love is a Flame by Gary Chapman The Four Lives by C.S. Lewis Love and Respect by Emmerson Eggerichs For the Right Reasons by Sean Lowe