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.

  • Caterpillar
  • China MediaExpress Holdings (Nasdaq: CCME)
  • Cliffs Natural Resources (Nasdaq: CLF)
  • Universal Display (Nasdaq: PANL)
  • Stillwater Mining (NYSE: SWC)

Some of these names might surprise you. For example, heavy equipment operator Caterpillar has been bulldozing a path to global economic growth for decades. Almost great? Even familiar names can still offer some of the best opportunities. Perhaps we've just forgotten the potential they still hold.

And with a populace that's growing wealthier the more it embraces free enterprise, Chinese companies are finding new ways to reach consumers. China MediaExpress Holdings operates the largest television ad network on intercity buses while Focus Media and VisionChina Media (Nasdaq: VISN) compete for an expanding slice of the out-of-home media market. However, the 160,000-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?
Doubts about international growth opportunities are playing on all mining, metals, and commodities stocks, even as concerns about Australia's "super tax" on mining companies raises special concerns for Cliffs Natural Resources, BHP Billiton, and Rio Tinto (NYSE: RTP). Shares in these companies have fallen off a cliff since the tax scheme was announced.

Although it's ostensibly a North American miner, Cliffs does have hefty exposure to Australia and China, and any actions that impede expansion there will fall to its bottom line. CAPS member tweetypielori is worried that the Australian mining tax will continue sending investors fleeing for safer havens:

If Australia imposes a 40% tax on any profits Cliff or any other producer has, more and more people will sell their Cliffs and look for something in another country that isn't imposing this tax. I am holding on for the ride in hopes that it won't pass. 

On the shoulders of giants
Ever since the dim bulbs in Congress outlawed regular incandescent lightbulbs (they'll be phased out by 2014), compact fluorescents such as those made by General Electric and Phillips have grown in popularity. LEDs have so far still proven to be too expensive to become mainstream, but by the time they do become affordable, we may already be enjoying the brighter prospects of organic LEDs made by Universal Display.

We're already seeing Samsung using OLED patents from Universal to manufacture cell phones, MP3 players, and TVs for which it is becoming the leader. CAPS member daniellpops sees Universal sitting on a "goldmine," while DarthMaul09 is looking for OLEDs to be the replacement TV of choice:

After the next big market crash, when all those poor defenseless monitors get trashed by their irate owners then [Universal Display's] energy efficient monitors will be the replacement of choice.

A big opportunity
As the only U.S. producer of palladium and the largest producer of platinum metals outside of South Africa and Russia, Stillwater Mining has the chance to capitalize on the resurgent auto industry. Analysts had been looking for the price of the key metal for autos to rise, but the events unfolding in Europe have traders rethinking the demand scenario as palladium prices are off 20% for the week. Fortunately electronics and jewelry are also big markets for the metal and with the tech sector hot and luxury no longer a dirty word, there may be plenty of outlets for Stillwater's supply.

CAPS member tcpprog says if the palladium miner can put together some consecutive strong performances the stock should follow suit:

Efficient and well run US miner is recovering from downturn of last two years, mostly in palladium and platinum. Looking for a string of strong quarters and this stock should take off.

A great opportunity for you
Investor sentiment suggests these four-star investments are 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.

Universal Display is a Motley Fool Rule Breakers choice. Try any of our Foolish newsletter services today, free for 30 days.

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.