Is there a single no-brainer investment?

As a matter of fact, there is - thanks to a nifty invention known as a target-date or life-cycle fund. These funds are perfect for investment-phobes. All you have to know is the date you intend to retire. Say you're 40 now and want to retire when you're 65. You pick a target-date fund whose date is the year you turn 65 - that is, 25 years from now.

Based on that information, the fund will do all the work for you, essentially creating an entire retirement portfolio in one fund. When you're younger, the fund will invest mostly in stocks, in order to take advantage of stocks' superior long-term growth. As you get older, it will gradually shift more money into bonds to take advantage of bonds' greater stability. It may throw some cash into the mix as your retirement date approaches. Voila - you're set.

Some critics may carp that fees for these funds are higher than they should be. But, hey - investing in one of them is a heck of a lot better than choking completely and leaving everything in a money-market fund (or, worse yet, in risky investments you don't really understand).