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 all the attention might be focused on their five-star peers, we can sift through CAPS to find four-star firms approaching greatness. Here are a few that are worth some attention.

  • Century Aluminum (NASDAQ:CENX)
  • Cepheid (NASDAQ:CPHD)
  • GMX Resources (NASDAQ:GMXR)
  • Johnson Controls (NYSE:JCI)
  • Stone Energy (NYSE:SGY)

Some of these names might surprise you. Automotive systems maker Johnson Controls hasn't steered the auto industry wrong (though the reverse may not apply). Almost great? Even familiar names can still offer some of the best opportunities. Perhaps we've just forgotten the potential they still hold. Since the 130,000-plus CAPS members chose these companies as less obvious sources for tomorrow's great buys, let's see why they might merit your attention.

In the sight of greatness?
It may be that the economic recovery everyone is hoping for is finally getting a foothold. Although there's every reason to ridicule the current euphoria as a "sucker's rally" -- after all, unemployment remains high, consumer spending has shown little strength, and GDP has plummeted -- there may be more to it than spring fever.

Manufacturing indices, for example, show contraction occurring at slower rates, meaning the situation is extremely fragile. The results of the so-called "stress tests" that banks were put through will be released soon, which may send confidence back down, but there may be enough passing grades to indicate that only those institutions we already knew were ailing are still sick.

There are other rising indicators as well. A Chinese think tank forecasts that economic activity in that country will rise to 7% in the second quarter, above the 6.1% increase seen in the first. That might signal demand for industrial orders. Caterpillar (NYSE:CAT) reported last month that infrastructure spending in China was igniting demand for bulldozers and earth-moving equipment. Raw-materials demand and pricing may soon follow suit.

That's part of the target on which investors in Century Aluminum need to pin their hopes. The aluminum producer has shut down potlines at its Ravenswood facility, as prices cratered after their extraordinary run last year. Workers have been laid off, and management reported additional earnings disappointments with an economy that's gone cold. Things haven't been much better over at Alcoa (NYSE:AA), which has a 50% stake in a joint venture with Century at a South Carolina plant.

Yet LME aluminum prices are on the rise again, approaching their level at year's end. Chinese aluminum output rose 30% sequentially in March, and increased 18% year over year for the same month. Century believes that some of China's smelters have restarted capacity, though it expects further cuts outside the country.

Such turns in fortune have some investors believing that aluminum in general -- and Century in particular -- has seen its nadir and will rebound from here. CAPS member manaburrn noted last month that pricing was on its way back, and with an otherwise firm balance sheet, Century should soon follow:

~ Aluminum is on the way back up from its bottom
~ Very strong balance sheet
~ Only $3 up from it's 52 week low, but $76 down from it's high.

A great opportunity for you
With four-star investments seemingly on their way to five-star greatness, 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.

Fool contributor Rich Duprey does not have a financial position in any of the stocks mentioned in this article. You can see his holdings here. The Motley Fool has a disclosure policy.