This New York Times article
has an interesting portfolio to consider:
[The Larry Portfolio] tracks indexes that achieved nearly the same 10 percent annual return between 1970 and 2010 as a portfolio invested entirely in the Standard & Poor’s 500-stock index. And here’s the Larry Portfolio’s trick: It did so with less than a third of its money in stocks, with the rest in one-year Treasury bills.
Seems like one could replace one-year Treasury bills with CDs for even less risk and slightly better returns. That would especially be the case in today's environment when 1-year Treasuries have yields of only around 0.12%.
My Money Blog has a good review
of this NYT article.