Macrotrends
macrotrends.net
A financial and economic data visualization site with 50+ years of historical charts for stock prices, P/E ratios, economic indicators, commodity prices, and interest rates — all freely accessible.
Why it is useful
The best free source for long-horizon financial charts. S&P 500 P/E ratios going back to the 1870s, unemployment rates since the 1940s, crude oil prices since 1861 — data that would otherwise require Bloomberg or expensive subscriptions. Charts are downloadable as CSV. Particularly useful for macroeconomic research and putting current financial conditions in historical context.