Here's an interesting blog post on the Harvard Business Review site on how money and motivation are related: they're not.
The results indicate that the association between salary and job satisfaction is very weak. The reported correlation (r = .14) indicates that there is less than 2% overlap between pay and job satisfaction levels. Furthermore, the correlation between pay and pay satisfaction was only marginally higher (r = .22 or 4.8% overlap), indicating that people's satisfaction with their salary is mostly independent of their actual salary.
In addition, a cross-cultural comparison revealed that the relationship of pay with both job and pay satisfaction is pretty much the same everywhere (for example, there are no significant differences between the U.S., India, Australia, Britain, and Taiwan).
It puts a little more solid evidence around the argument that is made in books like Daniel Pink's Drive: The Surprising Truth About What Motivates Us.