Sources of data and related tools
A Periodic Table of Visualization Methods
How Much Is That? - EH.net site for exploring the value of various currencies over time
U.S. Bureau of Labor Statistics - well organized, searchable data, including historical time-series.
FRASER, Federal Reserve Archive System for Economic Research - includes scanned images of historical economic statistical publications, releases, and documents (e.g., the Fed's 1959 publication, All-Bank Statistics, 1896-1955, which compiled statistics not only on nationally and state chartered banks but mutual savings banks and, for the first time, unincorporated or private banks).
FRED - Federal Reserve Economic Data
NBER Macrohistory Database - mainly U.S., but some data for France, Germany, and the U.K.
OECD Statistics portal
U.S. Historical Census Browser, University of Virginia Library
U.S. Patent and Trademark Office - Patent Full-Page Images from 1790