In the latest look at stocks ordered by largest market capitalization, Russell 3000 component GenOn Energy Inc (GEN) was identified as having a larger market cap than the smaller end of the S&P 500, for example Alpha Natural Resources Inc (ANR), according to The Online Investor. Click here to find out the top S&P 500 components ordered by average analyst rating Market capitalization is an important data point for investors to keep an eye on, for various reasons.