Market Capitalization to GDP
This indicator has been described by Warren Buffet as "probably the best single measure of where valuations stand at any given moment." It compares the total price of all publicly traded companies to GDP. This metric can also be thought of as an economy wide price to sales ratio.
The data here is from the St. Louis FRED. However, because the data is quarterly, we filled in the other months with the prior ratio adjusted for the change in stock prices.