The Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel 2011 was awarded to Christopher Sims (Princeton) and Thomas Sargent (NYU) "for their empirical research on cause and effect in the macroeconomy".
Once again Armen A. Alchian was overlooked despite his seminal and influential contributions to economics - see, for example, his 1972 American Economic Review article and his 1950 Journal of Political Economy article. His 1972 article with Harold Demsetz was one of the most influential articles published in the AER's first 100 years - see here. Notably, neither of the 2011 winners make this list.