Many people use a handful of Exchange Traded Funds to get an idea where the stock markets are going. The following list is a set a very popular ETF's used because they represent a wide range of companies.
Consumer Discretionary XLY
Technology Select Sector XLK
Industrial Select Sector XLI
Materials Select Sector XLB
Energy Select Sector XLE
Consumer Staples Select Sector XLP
Health Care XLV
Utilities XLU
Financial Select Sector XLF