People Skills by Robert Bolton.
This is a great classic that covers listening skills, how to give feedback, assertiveness, and conflict resolution. My most recommended book. So popular that the publisher has kept the cost quite low.
The Heart of Coaching. by Thomas Crane.
There are hundreds of books on giving feedback and performance management. This is one of the best.
The Coward's Guide to Conflict: Empowering Solutions for Those Who Would Rather Run Than Fight. by Tim Ursiny.
Good overview of why it is so difficult to handle interpersonal conflict, with some excellent self-directed exercises.
Difficult Conversations: How to Discuss What Matters Most.
by Stone, Patton and Heen.
A great summary of how to handle challenging conversations.
Hot Buttons; How To Resolve Conflict and Cool Everyone Down. by Sybil Evans and Sherry Suib Cohen.
Special emphasis on dealing with families and children.
Emotional Intelligence At Work. by Hendrie Weisinger.
A useful guide and workbook on a big topic.