Some companies are obviously great investments -- in hindsight. Yet for every stock out there screaming "buy me," others simply give us a nudge and a nod. How can we tell tomorrow's obviously great investments from the thousands of pretenders?

The stars' walk of fame
On Motley Fool CAPS, these opportunities can be found among our four-star stocks. In CAPS' proprietary ratings system, they rank higher than most of the other 5,300 starred companies, but they're just shy of superstardom. While their five-star peers get the attention, we can sift through CAPS to find four-star companies approaching greatness. Here are a handful.

  • AT&T (NYSE:T)
  • Merck
  • Monsanto (NYSE:MON)
  • NVIDIA (NASDAQ:NVDA)
  • United States Natural Gas (NYSE:UNG)

Some of these names might surprise you. Take AT&T, for example, With its history as long as telephony itself, not to mention its partnership with Apple (NASDAQ:AAPL) that gives it a great marketing edge, investors are right to ask: Almost great? Yes, even familiar names can still offer some of the best opportunities. Perhaps we've just forgotten the potential they still hold. However, the 135,000-plus CAPS members chose these companies as less obvious sources for tomorrow's great buys, so let's see why they might merit your attention.

In the sight of greatness?
Natural gas is a greener form of fuel than some others we've grown accustomed to using. It's plentiful, and drillers are exploiting ever-larger pockets. So it's probably a great investment vehicle all on its own. But if you're looking to harness the power of all those accolades, then put your money in Chesapeake Energy (NYSE:CHK) or place your bets with XTO Energy. Those are natural-gas plays.

At this point, that's not what United States Natural Gas is all about.

USNG is a commodities exchange-traded fund that tracks the underlying basket of securities and the futures contracts on natural gas. It also rolls its positions every month as contracts expire. More recently, however, it has been trading at a huge premium to its net asset value, and management has refused to issue new shares since July, when it ran out of its allotment of additional shares. Now USNG is trading more like a closed-end fund and has implemented a change in its investment strategy.

Futures pools, like USNG, need to issue shares on a regular basis to track the underlying shares. USNG got SEC approval to issue a billion new shares, but then the Commodity Futures Trading Commission began investigating whether speculators -- the bugaboo of Washington regulators these days -- were responsible for high gas prices. The CFTC may or may not be pointing its finger directly at USNG, but Citigroup says USNG controls a quarter to one-third of all open interest contracts on NYMEX and IntercontinentalExchange (NYSE:ICE) and is thereby creating abnormal demand and propping up prices.

With regulators considering new rules that would limit the size of positions that commodity funds can hold, USNG opted to not issue any more shares, because it could end up over those limits and would need to divest the ETF's positions.

In short, USNG is fraught with danger for the average investor, regardless of what the CFTC does. The risk, though, has nothing to do with natural gas as an investment and everything to do with how regulators are operating in Washington.

Do investors understand the risks? Although 97% of the more than 1,250 CAPS members rating the natural gas ETF mark it to outperform, CAPS member bladedog realizes that its premium is untenable. Another member, herztical, seems to understand the situation and blogs that a more market-based approach would let things work out naturally. He remains a USNG bull.

Finally, as with any asset class, the market will correct itself if it swings too much to one side or another. If we can take anything away from last [year's oil] spike and subsequent collapse is that eventually true supply and demand will dictate … price accordingly. Besides, do we really need more government interference and regulation? I say let the market decide if it wants these etfs around. If they don't prove themselves, well then there is no need to worry about regulating them because they won't be around for long.

A great opportunity for you
Investor sentiment suggests that these four-star investments still seem to be on their way to five-star greatness, but it pays to start your own research on these stocks on Motley Fool CAPS. Read a company's financial reports, scrutinize key data and charts, and examine the comments your fellow investors have made -- all from a stock's CAPS page.

Sign up today for the completely free service, and let us hear what you have to say about the great -- and almost great -- companies that interest you.

NVIDIA is a Motley Fool Stock Advisor selection. Chesapeake Energy is a Motley Fool Inside Value recommendation. The Fool owns shares of Chesapeake Energy and XTO Energy. Try any of our Foolish newsletter services free for 30 days.

Fool contributor Rich Duprey owns shares of Merck but has no financial position in any of the other stocks mentioned in this article. You can see his holdings. The Motley Fool has a gold-plated disclosure policy.