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 5,400 rated 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 companies that might become great. Here are a handful (CAPS ratings as of April 5):

  • AK Steel (NYSE: AKS)
  • CONSOL Energy (NYSE: CNX)
  • Flextronics (Nasdaq: FLEX)
  • Gastar Exploration (NYSE: GST)
  • Idenix Pharmaceuticals (Nasdaq: IDIX)

Some of these names might surprise you. For example, coal company CONSOL Energy was just one of two big names making major moves in the Marcellus shale region. Almost great? Even familiar names can still offer some of the best opportunities. Perhaps we've just forgotten the potential they still hold.

For example, it was something of a blow to Idenix Pharmaceuticals after Novartis decided not to exercise an option to license its hepatitis C therapy IDX184, causing the small biotech to seek out new partners. With its stock down, it helped its cause recently by announcing positive mid-stage results on the drug.

Because almost 90% of the more than 200 CAPS members who rated Idenix picked it to outperform the broad market averages, no doubt they're expecting someone will step forward soon to become a partner.

Likewise, some of the 160,000-plus CAPS members chose these companies as less obvious sources for tomorrow's great buys, so let's see why some of them they might merit your attention.

In the sight of greatness?
AK Steel joined the list of companies getting hit by health-care reform. Although AT&T's (NYSE: T) $1 billion charge related to the law is the heftiest one so far, AK Steel's $31 million charge isn't small change. Congress wants to haul a coterie of executives before the body to question them about their charges, because previous estimates showed that there should be reduced costs for large companies, as opposed to these enormous write-offs. That hearing is supposed to take place April 21.

Some investors remain concerned about health-care reform's impact on corporate profits. But 90% of CAPS members rating AK Steel apparently believe it will overcome any possible hits to the bottom line and beat the market's own performance.

On the shoulders of giants
Health-care reform has been divisive, but President Obama's decision to expand domestic offshore drilling for oil and gas is a lot more popular, and CAPS member getrichdietrying writes that oil and gas exploration company Gastar Exploration will benefit from the decision.

The company reported a fourth-quarter profit, helped in part by the sale of Australian assets. Yet with oil prices rising and natural gas off its lows, Gastar might be able to continue reporting profits, based on its operations. It probably wouldn't hurt, either, if the Energy Department's planned changes to its accounting of gas supplies results in lower inventory numbers. The reported gas glut has been part of depressed prices, and the DOE says it may have contributed by overestimating supplies. The accounting change might not be a dramatic one that results in gas prices soaring, though it ought to give us a more realistic picture of where the industry stands.

With 96% of CAPS members rating Gastar Exploration picking it to outperform, they might also benefit from changes that might cause prices to rise.

A big opportunity
The recovery in manufacturing might best be exemplified by the improving prospects of Flextronics, an electronics manufacturing services company that recently built a plant in Brazil with Research In Motion (Nasdaq: RIMM) and won a solar cell contract with Germany's Q-Cells.

CAPS All-Star musclemilk13 said last month that once Flextronics cleans up its balance sheet, it can take full advantage of these opportunities.

i think this will be a good long term hold and in time will clean up its balance sheet. its [price]/sales is currently .25, Forward P/E of 9 about a PEG of about 1. Definitely a riskier play due [to] its lesss than pristine fundamentals/balance sheet but from the reports I have read this is a solid company. 

A great opportunity for you
Some investors suggest 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.

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