Also, Never Split The Difference is basically a negotiation-oriented, machismo-tinted version of Nonviolent Communication by Dr. Marshall Rosenberg. I highly recommend both books.

Totally agree! Other similar books using similar models:

Connect, by David Bradford and Carole Robin (on business and personal relationships)

How to Talk so Kids will Listen and Listen so Kids will Talk (on parenting)

It's funny how at the end of the day, all interpersonal relationships work the same way, isn't it :-)