Founded in 1920, the National Bureau of Economic Research is a private, nonprofit, nonpartisan research organization dedicated to promoting a greater understanding of how the economy works. The Penn World Tables (country-level comparative indicators, 1950-2002) are here, along with the NBER Macrohistory database, industry data, international trade data, and other time series, and special topic datasets, mostly focusing on the United States.
Freely available data on internet.