These funds like to invest in companies that the market has overlooked. Managers like Marty Whitman of Third Avenue Value search for stocks that have become "undervalued" -- or priced low relative to their earnings potential.

Sometimes a stock has run into a short-term problem that will eventually be fixed and forgotten. Or maybe the company is too small or obscure to attract much notice. In any event, the manager makes a judgment that there's more potential there than the market has recognized. His bet is that the price will rise as others come around to the same conclusion.

Whitman, for instance, bought real-estate insurance company First American Financial early in 1997 before it was discovered by the Street. The stock rose 96% in 1998 and still traded at just 9.5 times the past 12-month earnings -- a steal when you consider the market average at the time was more like 22 times earnings.

The big risk with value funds is that the "undiscovered gems" they try to spot sometimes remain undiscovered. That can depress results for extended periods of time. Volatility, however, is quite low, and if you choose a good fund, the risk of doggy returns should be minimal. Also, because these fund managers tend to buy stocks and hold them until they turn around, expenses and turnover are low. Add it up, and value funds are most suitable for more conservative, tax-averse investors.