This site aims to 'make available to the public the highest quality and most reliable historical data on important economic aggregates, with particular emphasis on nominal measures.' Data is available for the US and the UK in addition to Japan and China with new series from other countries to be added. Calculators offer the ability to calculate relative values and purchasing power based on the 4 currencies for the countries mentioned above in addition to inflation rates, stock growth rates etc. Datasets (some available from 1790 to the present day) include GDP, CPI, price of gold, interest rates. There's also a graphing facility to track chosen variable values between two points in time and a user guide.
1790 - present day
Freely available data on internet