If you believe that the economy is growing and things are fundamentally OK here, then you should probably invest in index funds in the stock market.
S&P 500 buys/sells the stocks of the 500 largest companies in the U.S. (world?) It gets adjusted as the top 500 companies change. This strategy is good if you think that the biggest companies rule. Over long periods of time, it does really well, but does very badly when business conditions aren't favorable to big companies. The S&P did very badly from 2001-2002, but started getting better late 2003, and was on a tear in 2003, until the Federal Reserve started rattling the Sabres about interest rates.
There are "broader" market index funds, that cover 2000 and 5000 companies, if you want to work from a larger base.
Money markets are safer, but don't earn as much return.
If you believe the economy is unstable, that we have too much debt, and that we can't support future obligations, then you would probably want to opt for a more conservative approach, like bonds or even gold and silver.
I'm beginning to lean towards gold/silver because I don't like the fundamentals in our economy right now. I don't see how our economy can continue with any kind of sustainable growth, because of our high debt, both federal and personal. We, as a country, are borrowing ourselves to ruin. We have huge promises in social security for the next 30-40 years to a large segment of our population. Wages are too high relative to the rest of the world, and our goods cost too much, in many cases our quality is lousy. Our business leaders are outsourcing in droves, looking to move work to lower wage countries. The low interest that many of us have used to reduce our mortgage costs is just about over. Two staples of the economy, milk and gas are way up in cost. You tell me how we're going to grow the U.S. economy over the next 40 years, with a consumer population that will need to spend less money. I just don't see how it can get any better than it is now, and it's actually been getting worse since 2001. Gold and silver protect you from the instability of government debt, from currency valuation changes, etc. It works if you perceive that the future is in an unstable currency and unstable government. I haven't completely made up my mind, but I'm going there pretty quickly. In times like 2001-2002, gold and silver have soared.
So, be a prophet, tell the future, and make your choice.
Glen Austin