There are several asset classes you can choose for your portfolio: Cash, stocks, bonds, real estate, commodities and currencies to name just a few broad categories. The key idea here is that different asset classes have different levels of risk and return, and the way you mix them in your portfolio will play a key role in determining your overall risk and return.
Stock funds are some of the most popular especially since equities are often a bit riskier.
SPDR S&P 500 ETF Trust (SPY) corresponds to the performance of the S&P 500 and is well diversified across sectors including energy, health care, industrials, materials, telecommunications, and more.
SPDR Dow Jones Industrial Average ETF (DIA) follows the DJIA as the name would suggest. This ETF is essentially a basket of the 30 blue chip stocks that make up the Dow Jones.
PowerShares QQQ Trust, Series 1 (QQQ) is correlated with the Nasdaq-100 Index and delievers tha same performance.
iShares Russell 1000 Index (IWB), iShares Russell 2000 Index (IWM), iShares Russell 3000 Index (IWV) are all components of the Russell 3000 though by now you have probably guessed the trend in this article...The iShares Russell 1000 takes the 1000 largest securities issuers and the iShares Russell 2000 takes the smallest.
iShares Core S&P 500 ETF (IVV) is another ETF that tracks S&P performance with component stocks weighted according to the float-adjusted market value of outstandig shares.
Vanguard Total Stock Market ETF (VTI) tracks the performance of the aggregate stock market.
iShares Core S&P SmallCap 600 Index (IJR) looks for investments to correspond to the S&P SmallCap 60 Index.