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 exist 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 all of the attention, we can sift through CAPS to find four-star companies approaching greatness. Here are a handful of them.

  • Biogen Idec (NASDAQ:BIIB)
  • CONSOL Energy (NYSE:CNX)
  • Covidien (NYSE:COV)
  • DepoMed (NASDAQ:DEPO)
  • Electro-Optical Sciences (NASDAQ:MELA)

Some of these names might surprise you. Biopharmaceutical Biogen Idec, for example, has established itself with a plethora of therapies, perhaps most notably Tysabri, to treat relapsing multiple sclerosis. 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?
Some of you might remember Billy Crystal's character Fernando from Saturday Night Live -- the guy who used to say, "You look mah-velous!" Another of his signature catchphrases was, "It's better to look good than to feel good," and that might describe how many people approach suntans and skin care. Despite the risks associated with the activity, we continue to bake and broil ourselves in an effort to develop a George Hamilton-like perma-tan.

And you know what those risks are, of course. According to the National Cancer Institute, there will be an estimated 68,720 new cases of melanoma in the United States this year, with an estimated 8,650 deaths. The percentage of people who develop melanoma has more than doubled in the past 30 years. As with most illnesses and diseases, though, early detection increases the probability of successful treatment. Cancer researchers say that melanoma can be cured if it's diagnosed and treated when the tumor is thin and has not deeply invaded the skin. If it's not removed at its early stages, the cancer cells may grow downward from the skin surface and invade healthy tissue. That's when it spreads to other parts of the body and becomes more difficult to control.

General Electric (NYSE:GE) and Siemens (NYSE:SI) currently manufacture PET/CT scanners to help in the early detection of melanomas. But Electro-Optical Sciences is really shaking things up. In February, this medical-device maker announced clinical test results showing that its early-stage melanoma detection device MelaFind found 98% of the detectable melanomas in nearly 1,400 patients, all with no adverse side effects. The results promise to give doctors an accurate, objective method of diagnosing skin cancer, and the device itself ought to help doctors diagnose melanomas earlier. That advancement, in turn, should lead to a reduction in the number of potentially scarring biopsies.

After initially soaring some 88% after the announcement, Electro-Optical's shares gave back most of those gains in the following weeks. But they've marched ahead once again as the company prepares to file a pre-market approval application with the FDA for expedited review. The company has also received a commitment from a private equity firm for up to $45 million in financing over the next three years.

Investors are anticipating big things from Electro-Optical Sciences, and CAPS member kevquinn believes that the achievement of various milestones will push shares even higher:

melafind is an easy sell once it's been approved and because there is no side-effect attributable to it and because the data from the trials has been approved by a third party it should gain FDA approval. I expect three bumps in the next 7 months for this event driven stock. Eventually, I expect it to double the share price from current levels of six and a half.

A great opportunity for you
These four-star investments seem to 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's hear what you have to say about the great -- and almost great -- companies that interest you.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.