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's a handful:

  • AK Steel (NYSE:AKS)
  • EZchip Semiconductor (NASDAQ:EZCH)
  • Actuant (NYSE:ATU)
  • Petrohawk Energy (NYSE:HK)
  • Zoltek Companies (NASDAQ:ZOLT)

Some of these names might surprise you. AK Steel, for example, has been an iron-willed producer for years. Almost great? Even familiar names can still offer some of the best opportunities. Perhaps we've just forgotten the potential they still hold. However, the 130,000-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?
I learned my lesson the hard way about investing in good companies with questionable management when I lost a bunch of cash in aesthetic laser maker Candela. Even despite reporting the many shenanigans that management engaged in over the years, I held on to my shares way too long in the misplaced belief that the business would overcome the peccadilloes of those who ran it.

So, I'm a bit skeptical that carbon fiber manufacturer Zoltek Industries is really ready to pop or is on the road to a great future. CEO Zsolty Rumy is currently engaged in a bit of mud wrestling with an RBC Capital Markets analyst who has a decidedly negative opinion of the company. The situation got to the point that Zoltek issued a press release yesterday to combat what it says was "misinformation" put out by an analyst "with an axe to grind." It's rarely a good sign when management deems it necessary to take on an analyst; running the business right ought to disprove any analyst inaccuracies.

Yet the RBC analyst was right on at least one occasion, when he estimated that third-quarter earnings last year would fall well below consensus estimates. Despite management's contention at the time that its business was fundamentally sound and the analyst mistaken, profits came in far below even that gloomy assessment. Reduced customer shipments were the problem then, and customer order postponements and cancellations were behind the most recent results coming in below expectations. As he often has, CEO Rumy maintains that the fundamentals of the wind-energy sector remain brisk, with the potential to keep growing at an annual 20% to 25% rate. Similarly, when announcing Zoltek's preliminary full-year results last October, Rumy predicted it would be able to achieve a run rate of $500 million in sales by 2011. That's more than 2.5 times what Zoltek has generated over the trailing 12 months, and its revenue growth rates have been slowing.

Zoltek is a top carbon fiber producer for wind turbines and has long-term contracts with some of the industry's top manufacturers, such as Vestas Wind Systems and Gamesa. It has also announced plans to expand its offerings to deep-sea drillers, aerospace manufacturers, and car makers. It notes that Tesla Motors' new, sporty, all-electric vehicle uses Zoltek carbon fiber for its entire car and that General Motors' (NYSE:GM) Corvette uses the fiber in specialized areas. The poor state of the car industry, however, can't offer much encouragement as a growth opportunity these days.

Although Zoltek's shares are 75% below its 52-week high, it still trades at more than 50 times earnings. Compare that to rival Hexcel (NYSE:HXL), which has shares that are similarly depressed but a P/E of just 6.5, and it's easy to believe that Rumy's exuberance about his company's potential might be a bit inflated. Whereas Zoltek's revenue growth rates are on the decline, Hexcel's are accelerating.

Investors remain intrigued by Zoltek, however. CAPS member nelsonic72 is skeptical about management but finds its industry-leading position too solid to pass up:

Questionable management, but the stock is so beaten down and is still one of the better positioned carbon fiber companies going forward.

Warren Buffett once noted, "When a management team with a reputation for brilliance tackles a business with a reputation for bad economics, it is the reputation of the business that remains intact." I imagine he'd have similar feelings if the roles were reversed.

A great opportunity for you
These four-star investments could be on their way to five-star greatness, and 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 here. The Motley Fool has a disclosure policy.