I've found the following books very helpful:
Crucial Conversations - Its about conversations in which opinions differ, emotions run high and stakes are high (or not). I found this ot be very helpful skill to practice--to learn to deal with these sorta conversations which can happen outta the blue.
Difficult Conversations - There's two books with this name. One is by Anne Dickson which is ok, and the other one is by a bunch of people form the Harvard somthing Project. The second one is supposed to be excellent.
As I understand it, there's also another book called Fierce Conversations, about the same thing.
Another book I've found to be really fantastic for improving overall communication is Messages: The Communication Skills Book. REALLY good stuff in there, about a whole bunch of situations and settings and stuff. Very good for laying the blueprint of communication, and you can fill in the rest of it with specific books, such as how to approach people (as in books about networking) or how to argue/have difficult conversations while still keeping the relationship healthy and safe. Really fantastic book. Here:
Amazon.com: Messages: The Communication Skills Book: Books: Matthew McKay,Martha Davis,Patrick Fanning