This is an interesting, quick survey on motivation at Dan Pink’s website.
Dan Pink is the author of the excellent book Drive: The Surprising Truth About What Motivates Us
Type I behavior: A way of thinking and an approach to life built around intrinsic, rather than extrinsic, motivators. It is powered by our innate need to direct our own lives, to learn and create new things, and to do better by ourselves and our world.
Type X behavior: Behavior that is fueled more by extrinsic desires than intrinsic ones and that concerns itself less with the inherent satisfaction of an activity and more with the external rewards to which that activity leads.
One interesting observation: When most people think of productivity, they almost immediately tend to think in terms of Type X. Ironically, Type X is horribly detrimental to productivity in most cases. We are most productive (and, more important, enjoy what we are doing most) when we operate according to Type I.