For the emerging market equity portion of a portfolio, the iShares MSCI Emerging Markets Index (NYSEArca: EEM) is a low-cost, diversified fund that focuses on overseas economies. Another area that should be considered for proper equity allocation are the developed markets outside of North America. An index such as the MSCI EAFE Index represents developed markets in Europe, Australasia and the Far East, explains Gabriel. [ETF Spotlight: Vanguard Total Stock Market]

Next is the bond portion of a portfolio. Bond ETFs bring transparency and liquidity to the bond market by bringing them to the exchanges. ETFs also help make bonds more accessible for the masses. There are often high minimum investments and wide spreads associated with buying individual bonds. [Where is Our Friend, the Trend?]

A portfolio consisting of the four mentioned market segments can sustain a buy-and-hold ETF investor for some time. The maintenance needed would simply be to rebalance at least once per year. Morningstar suggests a good way to control turnover is to establish a rule that you will only rebalance the portfolio when a position has moved 15% away from the target weight. This can also help control transaction costs, which can add up if there are too many ETF trades taking place. [ETF Chart of the Day: Emerging Markets]

Tisha Guerrero contributed to this article.

Story updated to correct ticker for Vanguard Total World Stock Index ETF.