Some companies are obviously great investments -- in hindsight. Sure, we should have bought Starbucks at its IPO and earned hundredfold returns over the years. 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 companies in the CAPS universe, 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 approaching greatness:

  • Kinross Gold (NYSE: KGC)
  • Accuray (Nasdaq: ARAY)
  • Cree (Nasdaq: CREE)
  • Energy Conversion Devices (Nasdaq: ENER)
  • Potash Corp of Saskatchewan (NYSE: POT)

Some of these names might surprise you. Potash, for example, is a giant of a company in the fertilizer business, not only producing the most potash but also controlling 75% of the world's excess capacity. Almost great? Even familiar names can still offer some of the best opportunities. Perhaps we've just forgotten the potential they still hold. However, these companies were chosen by the 83,000 CAPS investors as less-obvious sources for tomorrow's great buys, so let's see why they might merit your attention.

An alternative investment
For Energy Conversion (ECD), it's been easier to turn sunshine into energy than it has been to turn its thin-film solar panels into profits. The company has consistently posted losses despite having a technology some consider superior to that of other solar companies -- it doesn't use polysilicon, which is currently hard to come by. If solar panels were all that ECD offered, that might be the end of the story, but many solar companies claim a technologically superior product. ECD would be just another in a large muddle.

Yet this solar company also has two other components that make it an interesting play nonetheless. ECD is developing rechargeable NiMH batteries for hybrid vehicles and various consumer devices. It is also a partial owner (with Intel (Nasdaq: INTC) of memory technology company Ovonyx, whose phase-change memory devices are someday expected to replace NOR memory, if not NAND and DRAM as well.

So, ECD has the potential to enjoy multiple revenue streams from these products. If any (or all) of them were to become more mainstream, those streams of red ink ECD is currently producing just might flow green.

The bull case
CAPS investor familyfund1 covers all the basics in the top bull pitch, written at the end of last year. The pitch also notes that the company has scored some impressive contracts recently, and that the stock enjoys substantial insider and institutional support.

United Solar Ovonic, a wholly owned subsidiary of [ECD], building on technology invented and pioneered by [ECD], is the world leader in thin-film amorphous photovoltaics. Because of characteristics unique to the United Solar Ovonic solar cell technology, such as lightweight, ruggedness and flexibility, it is ideal as building-integrated photovoltaic roofing systems. ECD and United Solar Ovonic hold the basic patents covering the continuous roll-to-roll manufacturing of thin-film amorphous-silicon alloy multi-junction solar cells and related products. ... They also have [a] neat patent for memory chips.

Read the full pitch here.

The bear case
While 92% of the investors rating ECD think the company will outperform, several dozen investors still scoff at this company being a success. The bear side might best be summed up by CAPS player colleran, who can't understand how ECD has been able to attract investors for so long.

Why this company is still in business is beyond me. ... I don't see any possibility in the future. NiMH batteries are being bypassed by Li-ion and Fuel Cells are unlikely to be profitable in the next 20 to 30 years, if ever.

A great opportunity for you
You've heard the latest on ECD, but do you agree? Are these four-star stocks still investment-grade material? On Motley Fool CAPS, you can give your input, which can ultimately influence how they're rated. Outperform or underperform, near-term or well into the future, your opinion counts.

Sign up today for Motley Fool CAPS -- it's completely free. Let us hear what you have to say about the great (and almost great) companies that interest you.

Intel is a recommendation of Motley Fool Inside Value. You can take a 30-day free trial of any of the Fool's investment services.

Fool contributor Rich Duprey owns shares of Intel, but none in any other stocks mentioned in this article. You can see his holdings here. Starbucks is a Stock Advisor selection. The Motley Fool has a disclosure policy.