SPDRs
Usually referred to as spiders, these investment instruments bundle the benchmark S&P 500 and give you ownership in the index. Imagine the trouble and expenses involved in trying to buy all 500 stocks in the S&P 500! SPDRs allow individual investors to own the index's stocks in a cost-effective manner.

Another nice feature of SPDRs is that they divide various sectors of the S&P 500 stocks and sell them as separate ETFs, there are literally dozens of these types of ETFs. The "technology select sector index", for example, contains over 85 stocks covering products developed by companies such as defense manufacturers, telecommunications equipment, microcomputer components and integrated computer circuits. This ETF trades under the symbol XLK on the AMEX.