If you intend to invest for the long-ish term (at least a few years) I recommend vanguard.com's VFINX mutual fund, based on the S&P 500 index of 500 different large stocks. If this is for retirement you could set up a Roth IRA there instead of a regular brokerage account.
An S&P 500 fund is the investment that most other mutual funds compare themselves to, some do better but usually with much higher risk.
If you don't want to deal with vanguard.com, people are happy with scottrade.com and they sell many mutual funds (including other funds based on the S&P 500 index) as well as individual stocks.
If you only have a few hundred to invest, some people use sharebuilder.com.
If you are only investing for a short time (under 2 years) you might be better off just using a high-interest savings account from INGDirect.com or Emigrant.
(Advanced Search > invest stocks) for more opinions.
(edit) But ignore Looney's he was just being silly. If you could go back in time and invest 200K in Microsoft in year 1 you'd be a billionaire that way too.