I Love You But Why Are We So Different Author:Tim LaHaye Making the Most of Personality Differences in Your Marriage
Temperaments expert Tim LaHaye delves into the four basic personality types to help couples turn their personal differences into marriage–enriching assets. Biblical principles and practical advice encourage readers to build dynamic, lifelong relationships.
I have not read this book myself, but it was recommended from a friend when I was having issues in my marriage. Tim LaHaye is the author of the Left Behind series, and he is a smart man, so I am sure that this is a good book for relationships.