Just like caraudio, it depends on what your preferences are. higher risk, high expected return.
How safe? Currently, the i-bond pays around 6.7% (it is indexed to the interest rate, will go down if rate goes down) A good part is that there are no transaction costs. bad part is you have to hold for 5 years.
etf are alse pretty good. They work like mutual funds except you can have a smaller minimum investment because they trade like stock. I own a few in biotech and nano-tech because it is hard to determine which of the companies will come out with something revolutionary. Also allows investment in foreign countries with limited risk.
If you feek pretty risky, you can get into options, which is what I do. You either hit a homerun or you strike out. Occasionally a grand slam, occasionally tear an ACL kinda of deal. My other portion is in small caps...basically small companies that do one or two things, hoping one hits it big.
I would reccomend you invest in segments with etfs. The transaction costs are a little higher than a straight mutual fund but allows for diversification into segments of the market. Say, you wanted to focus on nasdaq tech stocks ---QQQQ is an etf that holds a weighted portion of the nasdaq 100. The Dow Jones Industrials -- DIA holds equal weights of all 30 dow jones companies...yahoo.finance.com could show a lot more about etfs. Without strong accounting and finance background or sheer nerve I wouldn't suggest investing in single stocks.
If you have anymore questions, PM me. I won't give any stock tips because I can't tell the future. I have no idea what stock will go up or down tomorrow, but I can tell you if I feel it is under or overvalued.