Among the best (most important listed first):

Gottman, John M. The Seven Principles for Making Marriage Work.1999. [One of the most solid books on marriage, this teaches core principles from extensive research.]

Chapman, Gary. The Five Love Languages: How to Express Heartfelt Commitment to Your Mate. 1995. [Sensible ideas for effectively showing love.]

Christensen, Andrew & Neil Jacobsen. Reconcilable Differences. 2000. [Acceptance is a vital part of good marriage]

Seligman, Martin E. P. Authentic Happiness. 2002. [How to be a flourishing human.]

Buehner, Caralyn and Mark. Fanny’s Dream. 1996. [A delightful children’s book for teaching principles of healthy relationships.]

Gottman, John. Why Marriages Succeed or Fail. 1994. [Discusses three kinds of relationships and the blessings and challenges of each.

Gottman, John M. The Relationship Cure. 2001. [Especially good section on bids, i.e., our efforts to connect, and the ways we can respond to bids.]

Gottman, John M. & Gottman, Julie Schwartz. 10 Lessons to Transform Your Marriage. 2006. [Ten case studies to help each of us see how to apply the principles that strengthen marriages.]

Goddard, H. Wallace & Marshall, James P. The Marriage Garden. 2007 at www.arfamilies.org. [Six lessons on key principles of marriage.]

Very good books (in alphabetical order by author’s last name):

Arbinger Institute. Leadership and Self-Deception: Getting Out of the Box. 2000. [Self-deception exacts a terrible cost at work and at home.]

Beck, Aaron T. Love is Never Enough. 1988. [Strong marriages require more than strong feelings. Ideas for changing the way you think about problems.]

Doherty, William J. Take Back Your Marriage. 2001. [Don’t let the world pull you apart.]

Fowers, Blaine J. Beyond the Myth of Marital Happiness. 2000. [Insightful book about the importance of values in sustaining marriage.]

Glass, Shirley P. & Jean Coppock Staeheli. Not “Just Friends”: Protect Your Relationship from Infidelity and Heal the Trauma of Betrayal. 2003. [Affairs can be prevented or overcome.]

Stanley, Scott. The Heart of Commitment. 1998. [Commitment is a key to a strong relationship.]

Van Epp, John. How to Avoid Marrying a Jerk. 2007. [By using good sense--and by managing level of commitment, anyone can make a better choice.]

Waite, Linda & Maggie Gallagher. The Case for Marriage. 2000. [Describes the many benefits of marriage.]

Warner, C. Terry. Bonds that Make Us Free: Healing Our Relationships, Coming to Ourselves. 2001. [When we refine our motivations, we will have better relationships.]

Weiner-Davis, Michelle. The Divorce Remedy. 2001. [How to strengthen your marriage and prevent divorce.]

Weiner-Davis, Michelle. The Sex-Starved Marriage. 2003. [Physical intimacy is a challenge for many couples.]