Book by
Daniel P. Goleman:
This is the book which put EQ on the map. It makes a good case for what Emotional Intelligence is, why it's important, and some of the brain science backing it up (along with scientific support for NLP concepts like rapport). No clues given as to how to develop it though! I found the book readable and fascinating (though as I teach EQ development courses I have a professional interest). It's a good summary of much of the research in this area. (Andy Smith, London England, from Amazon.com)
At it's most basic level, emotional intelligence is about cultivating one's perceptions of emotions--that is, to learn to percieve emotion. In yourself (introspection) and others (empathy). From there, it's relatively straightforward to start reasoning with this information.
The next level may be more of a conceptual leap, and that is that emotions are not necessarily rational, but they are nevertheless valid. In fact, the more unreasonable they are, the more important it is to take a peek at what's going on with them.