Start with a basic diversification that would give you broad U.S. and international exposure, including some emerging markets plays, as well as some fixed income, depending on your risk tolerance, says Culloton. If you're a risk taker and have time on your side, you probably could afford to go all-equities. If not, Culloton recommends that 10% to 30% be in fixed income.
For your U.S. exposure, the Vanguard Total Stock Market VIPERs (VTI) and the iShares S&P 500 Index (IVV) are relatively cheap. The iShares Russell 3000 Index (IWV) is also worth checking out, since its expense ratio is just 0.20%.
On the international front, consider the iShares MSCI EAFE Index Fund (EFA), suggests Culloton. This ETF mirrors the Morgan Stanley Capital International Europe, Australia and Far East Index (MSCI EAFE) index and is composed of about 1,000 companies that trade on 20 stock exchanges around the world (not including the USA, Canada, and Latin America). Can't get much more international than that. For emerging markets, there's the Vanguard Emerging Markets Stock VIPERs (VWO), which is cheaper than its iShares counterpart.
If your ulcer (or common sense) requires some fixed income in your portfolio, check out the iShares Lehman 1-3 year Treasury bond (SHY). Especially with the interest rate uncertainty out there, fixed income could be a wise choice.