Another solid choice, especially if you're worried about inflation, is the iShares TIPS Bond ETF (NYSEMKT: TIP) , which invests in government-issued, inflation-protected bonds. As a general rule, I often suggest that investors subtract their age from 110 to determine their appropriate stock allocation, and the rest of their portfolio should be in bonds. The Vanguard Total Bond Market Index Fund ETF (NYSEMKT: BND) is one smart choice.