The actual list of all 500 stocks in the S&P 500 is called the Constituent List. It can be found on the official Standard & Poor's website under the Equities Indexes section.
To be added to the S&P 500, a stock must meet a broad spectrum of criteria, including a total market capitalization of at least $5 billion. Additionally, the stock must be issued by a U.S. company, have four consecutive quarters of positive earnings, and also meet certain liquidity requirements. Companies may be removed from the S&P 500 if they deviate substantially from these standards.
Unknown to most investors is the fact that the S&P 500 is a market capitalization weighted index. This means that the more valuable an individual company's stock becomes, the more it contributes to the S&P 500's overall return. It is not uncommon for three-quarters of the index's return to be linked to only 50 to 75 stocks. Hence, the addition or subtraction of smaller companies from the index most likely will not have a noticeable impact on the overall return of the index.