Positive Psychology News Daily recently ran this article recommending the Happiness Hypothesis, which happens to be one of our favorite happiness related books as well. I find the metaphor of the elephant and the rider useful as well, though for different reasons as this author. Specifically, I find that it's useful to be aware that our minds are like trainable animals that we can only control indirectly.
If you have not read it, I highly recommend Jonathan Haidt’s The Happiness Hypothesis. One of Haidt’s metaphors, more thoroughly explained in the book, is the very accessible image of the rider (conscious reasoning self) and the elephant (automatic and unconscious self).