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 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 handful of four-star firms approaching greatness:

  • Alcoa (NYSE: AA)
  • Celgene (Nasdaq: CELG)
  • Cliffs Natural Resources (NYSE: CLF)
  • Halliburton (NYSE: HAL)
  • iShares Silver Trust (NYSE: SLV)

Some of these names might surprise you. For example, oil fields expert Halliburton has been an industry leader for 80 years. Almost great? Even familiar names can still offer some of the best opportunities. Perhaps we've just forgotten the potential they still hold.

That would be similar to how silver gets lost in the bright glare of gold. SPDR Gold Trust (NYSE: GLD) may have grabbed headlines and returned more than 60% over the past two years, at a time when the market itself has fallen by around 10%. Yet iShares Silver Trust did even better, soaring over 80% over the same time frame.  However, the 170,000-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?
We know earnings season is upon us when Alcoa reports its quarterly results. The first Dow Jones industrial stock to tell us how it did and what it sees for the future is seen as something of a bellwether company, not only because of its off-to-the-races start for earnings, but also because aluminum is a key metal for industry. If business isn't buying what Alcoa is selling, then the rest of the earnings season is likely to be dour, too.

Yet Alcoa's last earnings report would suggest that even if "recovery summer" was "recovery bummer," we might not be so far from the turnaround we've been hoping for. Despite lower pricing for the metal, the top aluminum producer saw revenue surge 22%, generating profits that were 8% higher than Wall Street's forecast. That's a 180-degree turn from last year's losses.

With more than 3,000 CAPS members rating Alcoa, perhaps it's not so surprising that 93% say it will outperform the broad market averages going forward.

On the shoulders of giants
With sales of Revlimid accounting for more than two-thirds of Celgene's second-quarter revenue, a generic rival for its treatment would seriously threaten its future performance. So when the biotech announced that someone had filed an application to bring a Revlimid generic to market, investors' shock was palpable.

Sales of the MS drug jumped 46% in the second quarter, helping Celgene grow overall revenue by 38%, and generating a 55% jump in profits. With its pending acquisition of Abraxis BioScience wending its way toward completion (along with its purchase of Gloucester Pharmaceuticals), Celgene will have a potent portfolio of cancer-fighting therapies. Celgene also offers its own oncology treatment, Thalomid, along with Vidaza, which is licensed from Pfizer (NYSE: PFE) and saw its own impressive 43% increase in sales. With such a strong lineup, any weakness investors find in its stock just might be an opportune time to step in.

Celgene's growth potential through acquisitions attracted CAPS member TheStreetOutside, who believes its stock is a value:

Big cap biotech company with very promising future, what I expect to be very succesful acquisitions, and yet nearing a 52 week low. Value play and a possible acquisition target as always.

A big opportunity
While an economic rebound is by no means assured, the engine driving the economy forward will need steel. That means demand for iron ore will rise, playing right into the hands of Cliffs Natural Resources, North America's largest ore producer. If ore prices start marching higher, as analysts suggest, expect Cliffs to rise as well. Highly rated All-Star CAPS member Beorn10 certainly does:

Domestic steel production is still needed to help rebuild our industrial manufacturing base. CLF should benefit from this need.

Cliffs recently bought INR Energy, expanding its production of coking coal -- another key steelmaking ingredient -- to 11 million tons by 2012. With analysts estimating that coking coal prices will also rise this year, it's hard not to see Cliffs sitting pretty.

A great opportunity for you
Investor sentiment suggests these four-star investments still seem to be on their way to five-star greatness. Still, 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 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 gold-plated disclosure policy.