Their joint paper Business cycle modeling without pretending to have too much a priori economic theory has stood the test of time.
I clearly remember the excitement I felt when reading it around 10yrs ago. It precisely formulated some of my discomfort with Macro models, and introduced me to factor analysis.
Sims’ Macroeconomics and Reality has also stood the test of time.
These are both methodological papers – which is what earned them their award. However, both have also made very practical contributions, on relevant current issues.
Sargent recently published on the break-down of the correlation between inflation and nominal interest rates (the return of the Gibson paradox).
Sims (the smarty pants) showed back in 1999 that the Euro was incomplete, and would need additional institutions to survive. See his