Greg Mankiw asks and receives many answers.
One guess is William Nordhaus, for his concept of "green accounting." An environmental prize is overdue but perhaps Nordhaus is too skeptical about stringent anti-global warming measures to get the appropriate reception in Stockholm.
Another option is Eugene Fama, both for testing CAPM for securities prices and for figuring out what is wrong with it. You can imagine pairing his prize with either Richard Thaler (behavioral finance) or Kenneth French (Fama’s co-author on many important papers).
Or how about Oliver Williamson and/or Jean Tirole for principal-agent theory as applied to the business firm?
I would offer the prize jointly to Anne Krueger, Jagdish Bhagwati, and Gordon Tullock for their work on rent-seeking, but that is not my prediction. Readers, what do you think?