I have to say that if there are two books that I really bought into completely, they'd be Dale Carnegie's How to Win Friends and Influence People and Robert Sutton's The No Asshole Rule. Carnegie's book covers how to be nice; Sutton's covers why organizations should be less tolerant of, er, "jerk" behaviors.
In addition to these sources, there are a number of resources, training sessions and workshops on how to communicate effectively, or on netiquette, or other related topics.
Yet, even with all these opportunities for enlightenment, I have witnessed otherwise-intelligent people read the books, attend the trainings, and still not get it. Why? Are they unaware of their behavior? It could be. Or do they not see the value of courtesy? If so, allow me to make the case against the "nice guys finish last" mentality...
1. People are more likely to cut you some slack if they like you. They may judge you more harshly if you have offended them in the past.
What may be small to you (good or bad) may be a big issue to someone else, and they may not forget it, especially if they have limited contact with you. If you paid a compliment to someone once, he or she may like you and go easy on you forever. If you made a bad impression in an email once, someone may be looking for another reason to be mad at you.
2. You may have chosen your career because you wanted to spend the next thirty years working solo in a basement, but collaborative tools and interdepartmental/cross-functional projects will make everyone a team-player at some point.
Firing off flames from the safety of your inner sanctum may have worked before, but think twice before doing it in today's work environment. You never know who might be a future team member; you may just be burning a bridge.
3. The world is flat. There is no hierarchy. There are no little people.
Be nice to everyone. You never know who might be on a search committee, who might recommend (or discredit) you to a friend, or who might be promoted to a position of greater authority.
I just saw this today. Polly LaBarre is also saying this, and cites research on the topic: http://www.mavericksatwork.com/?p=121