The most important measure of the financial strength of the United States is the Standard & Poor’s 500 stock index. It’s widely watched but constantly surprising. Of the 500 companies in the S&P 500, the five largest account for 21% of the total value of the much-watched index. You won’t believe where they are currently valued! Ranked by market capitalization, the five companies are: Apple, Microsoft, Amazon, Google, and Faceb..