Vanguard Group -- one of Clark's favorite companies -- is approaching nearly $1 trillion in investment dollars.

The Vanguard business model is virtually unique in the investment world. Vanguard is essentially a coop owned by account holders, which makes it much like a credit union for investing. Now The Wall Street Journal reports the company had more than $900 billion in long-term mutual-fund and ETF assets in its portfolio as of June.

Why exactly is business booming for Vanguard? Simply put, they offer a great deal.

There are two ways to buy a mutual fund. You can either buy from a commissioned salesperson where you pay a "load" fee, plus an annual management fee or you can buy a "no load" fund. The latter type is offered by Vanguard and involves no commission but still requires you to pay an annual management fee.

When it comes to management fees, a typical fee across the industry can be a little more than 1 percent. So you're paying a dollar and change in management expenses for every $100. But Vanguard's management costs are just one-sixth of the average. That's like paying a mere 20 cents on every $100.

People are wising up to the long-term costs that accompany investing. The fact is that you pay so much less for Vanguard to handle money for you. And paying lower expenses over time makes you more money in the long run.