At this very moment, I'd say gold and to a lesser extent real estate (in my unprofessional opinion). I don't trust brokerage companies to remain solvent in the event of a derivatives meltdown (which I expect within the next few years). Brokerage accounts tend to be insured privately, but if they all go down at once, the insurance won't help much. I expect interest rates to go up, so I don't like bonds or CDs much (at lest not the long term ones).
The best kind of investment is actually dependent on various factors, chief among them being the prevailing market conditions. On the whole, real estate and stocks are said to be great investments because they offer a good return. However, they are rather risky and require substantial investment to realize these returns. Talk to an investment Advisor for professional advice.