Love and Respect
Emerson Eggerichs
This is a powerful book on marriage that revolves around one verse in the Bible, Ephesians 5:33. It is a passionate call for men to love their wives sacrificially and for wives to respect their husbands lovingly. It is filled with practical applications.

His Needs, Her Needs
Will Harley
This is an excellent guide to the top marital needs for most men and the top marital needs for most women.

The Meaning of Marriage
Timothy Keller
Keller is always scholarly, always insightful, and often practical.  This may be the best overview of marriage.

Learning to Live With the Love of Your Life
Neil Warren
I find this book the overall most helpful book on marriage. Superb.