Below are my top book recommendations for couples (in no particular order).
The Seven Principles for Making Marriage Work by John Gottman
The Space Between by Harville and Helen Hendrix
The Unmade Bed by Stephen Marche
The 5 Love Languages by Gary Chapman
Wired For Love by Stan Tatkin
Getting the Love You Want by Harville Hendrix
Eight Dates by John and Julie Gottman
Men Are From Mars, Women Are From Venus by John Gray
Hold Me Tight by Sue Johnson