$Vanguard Total World Stock ETF (VT.US)$ The ultimate foreve...

$Vanguard Total World Stock ETF (VT.US)$ The ultimate forever investment with reliable returns is VT, the most thorough total global fund with low fees.

Of course its recent past returns aren't as good as those of VTI, but betting that the US will continue to outperform for decades is a bad bet.

You could then include small cap value funds if you want, and that would definitely increase expected return. But if you're trying to keep it simple, VT (or the mutual fund VTWAX) is a great fund.