Vanguard, a retirement provider that is well known for its low-cost funds, offers many diversified equity and bond funds. "Time is your greatest ally in investing," says Greg McBride, chief financial analyst at Bankrate, a financial data company. "For those in their 20s, every dollar you put away now can be worth $20 or $30 by the time you retire. That is the power of compounding doing the heavy lifting -- you put in $1 and compounded growth over a long period of time does the rest."