As the stock market turned rocky last year, Tim Koehler started paying attention to his mutual-fund fees.

The St. Louis software developer had relied on his financial adviser to select the mutual funds in his Roth IRA, and they all carried sales charges, or "loads," and annual expenses ranging up to well over 2%. "I felt I was just throwing money away," says the 32-year-old Mr. Koehler.

After...