Men are from Mars, Women are from Venus...John Gray. This classic book isn't for every couple, but if you read a few chapters and lightbulbs start going off, then its probably going to help you understand how communication with the opposite sex actually needs a roadmap.
The Seven Principles for Making Marriage Work...John Gottman. To me this book wasn't so much helpful in actually making marriage work, but rather in understand what marriage "poison" is and then you can find out how to avoid it.
Why Men Love Bitches...and No More Mr. Nice Guy. These books say basically the same thing to men and women: "gain his/her respect or he/she won't be sexually attracted to you, period".