I don't think it is going to be a field that we've named already.
It'll likely be some combination.
Nonotech and biotech are converging and influencing a lot of things rights now (including better materials, alternative energy, and fine-scale manufacturing).
Medical imaging and Computer Tomography are yielding new insights into the human body, especially the human brain. This in turn has filled the science section of book-stores with many books on the brain and the mind, as neuroscience is making great progress (backed by a co-discoverer of DNA, no less). Along with this there have been great strides in cognitive science which is tightly connected to Artificial Intelligence (which is an antiquated term for what has now become many sub-disciplines connected with things that are not necessarily confined creating an artificial form of "intelligence"-- including statistical inference, neural-networks, Fuzzy Logic, multi-modal formal reasoning, Modern Control Theory, pattern recognition, Human-Computer Interaction, Semantic Networks, ...).
I think Automation (Industrial, Corporate, and Domestic) is something that has had great potential for a long time. Imagine being a business owner simply having to do minimal maintenance to a "machine" that takes and fulfills orders--complete with custom manufacturing, automated delivery, and collection/analysis of customer feedback. But out labor market would go through a temporary crisis in "unskilled" work if an industry focused on automating everything were to flourish.
Right now information is cheap and getting cheaper exponentially, while energy remains about as expensive as it has always been (if not getting more expensive). So I think the greater potential is there for some break-through in energy.
Whether or not we'll have one is a different question.
We may only be able to make things slightly cheaper (long-run, remember we've passed peak-oil) with the use of 4-th generation nuclear, solar ink/paint, oil shale, and fuel-cell cell technology, hybrid and electric vehicles to use less of our scarce oil and more of our grid (mostly powered by coal).