Even though I am not (this year) on the list of potential nominators, if I were, I would nominate Richard Posner to receive the next Bank of Sweden Prize in Economic Sciences in Memory of Alfred Nobel.
He has, throughout his career, done more than any other economist to further the understanding of economic analysis of law in particular and economic analysis of anything in general. No topic has eluded his analysis, and he has brought a raft of tools, knowledge, and experience to every topic he has investigated. No matter what he studies, he always applies and extends basic economics: (1) people respond to incentives, and (2) actions and choices involve the use of real resources.
He has challenged myriad knee-jerk positions held by people of all political stripes, and he has had a major impact on how the courts apply economics in all their cases.
He was a founding editor of The Journal of Legal Studies, which extended the application of economic analysis beyond anti-trust and regulation, which had been the major areas of overlap until then. His text/treatise Economic Analysis of Law, now in its 6th edition, was a pioneering work. It demonstrated, more than any other work, how careful yet consistent application of economic analysis can elucidate legal principles, legal decisions, and the evolution of legal institutions. Through everything he has written, he has relentlessly applied The Economic Way of Thinking.
I know he has done a considerable amount of work in other fields (law!), but subtract all that work from his C.V. and you still have the contributions of someone who has clearly and substantially moved the frontiers of economics outward in major ways that will forever benefit the rest of society.
Here is his week-long diary that he published in Slate back in January, 2002. Here is a list of his 2003-04 output. and Here is his website at the Univ of Chicago Law School. And you can explore the list of his available books (e.g. Sex and Reason, his attack on public intellectuals, and his work on Aging and Old Age) by clicking this box if you are in Canada:
If the committee were to award the Nobel Prize in Economics to Richard Posner, it would not be the first time it awarded the prize to someone who was a not exclusively an economist by training. Others who come to mind are socionomist, Gunnar Myrdal (1974), and psychologist/political scientist/organization theorist Herbert Simon (1978).
Update: for more information about Posner, read this