Kydland and Prescott will receive the Bank of Sweden Prize in Economic Sciences in Memory of Alfred Nobel 2004"for their contributions to dynamic macroeconomics: the time consistency of economic policy and the driving forces behind business cycles". You can find more information on the Nobel web site. For those of us who can remember having read about business cycles in our macro economics courses but are in need a quick recap, there is a nice review of Kydland and Prescott's contributions to the literature.