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 companies approaching greatness, like these:

  • ATP Oil & Gas (Nasdaq: ATPG)
  • Berkshire Hathaway (NYSE: BRK-A)
  • Spectrum Pharmaceuticals (Nasdaq: SPPI)
  • Tesoro (NYSE: TSO)
  • Yongye International (Nasdaq: YONG)

Some of these names might surprise you. For example, the sky-high price of Warren Buffett's investment vehicle Berkshire Hathaway reflects both his investing acumen as well as that of partner Charlie Munger. Almost great? Even familiar names can still offer some of the best opportunities. Perhaps we've just forgotten the potential they still hold.

Although the environmental disaster unfolding at the site of BP's (NYSE: BP) Deepwater Horizon rig in the Gulf of Mexico has created a backlash against all drilling in the area, causing ATP Oil & Gas and industry equipment provider Dril-Quip to suffer the consequences, it seems unlikely this will mark the end of all deepwater drilling. However, the 165,000-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?
With two drugs already on the market, and rising sales of Zevalin, a monoclonal antibody chemotherapy for non-Hodgkin's lymphoma, Spectrum Pharmaceuticals is well ahead of other small-cap biotechs that hope to crack the market. Milestone payments from a partnership with Allergan might just make it a dream stock for those looking to invest in the niche.

While that hasn't been enough to prop up Spectrum's stock -- which is down 15% year-to-date and more than 25% in the past month alone -- investors remain exceptionally bullish about its long-term prospects. Over 98% of the 280 CAPS members rating the biotech mark it to outperform the broader averages.

CAPS member jlarpenteur says it doesn't have to hit the mark on each of its pipeline candidates to be a winner:

Clinical trials in two of its drug candidates will be completed soon and if just one suceeds, it should give rise to a substantial stock price increase. Further, sales of its existing products should dramatically increase in the next year also leading to stock price increases.

On the shoulders of giants
There was a bit of surprise when gasoline prices actually fell before the Memorial Day weekend. As the unofficial start of summer, it also typically heralds an increase in gas prices as drivers hit the nation's highways in greater numbers. But with concern about the fragile economy and uncertainty about the long range impact of the Gulf spill, oil prices have fallen.

That depressed demand for oil and gas has hit refiners like Tesoro and Valero (NYSE: VLO) particularly hard. As the "crack spread" narrows, the margins for the refiners come under increasing pressure. The spread comes from the industry benchmarks called the "3-2-1 crack," which determines the profits a refiner can make from "cracking" three barrels of oil into two barrels of gasoline and one barrel of heating oil.

Highly rated CAPS All-Star member goldminingXpert is looking for the spread to widen eventually, meaning today's lower price on Tesoro gives investors an excellent entry point:

Tesoro (which is the spanish word for treasure) is an attractively priced independent refiner at $12. With a history of sound operations and profitability, buying TSO guarantees you a decent return once the crack spread (difference between oil price and gas price) widens again. Assuming Americans will continue to want gas, TSO will eventually rally strongly. The crack spread has widened throughout 2010, and with the price of crude plunging now, we can expect profit margins to increase further. Assuming TSO gets a few good quarters under its belt, a speedy move to $16 or $18 is quite likely.

A big opportunity
Chinese feed and fertilizer maker Yongye International is counting on the continued, growing demand for food in its home country to keep it green and healthy. In its most recent quarter, revenues doubled, underscoring the previous notice it gave that it was raising its revenue forecasts for the rest of the year. It continues to look for sales of as much as $165 million.

CAPS member RedDoor9 says that since it operates mostly within China's borders, investors shouldn't feel the effects of any currency changes:

Cash rich company operating in booming sector of the fastest growing economy in the world. I liked their move to buy the supplier of one of their main product ingredients. The business strategy they employ to add new vendors at low costs should also be a strategic advantage. Plus, this stocks market is mostly domestic and should therefore not be disrupted by a revaluing of the renminbi. I think that this stock is a long term winner.

A great opportunity for you
Investor sentiment suggests that these four-star investments still seem to be 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.

Berkshire Hathaway is a Motley Fool Inside Value pick. Berkshire Hathaway is a Motley Fool Stock Advisor selection. Yongye International is a Motley Fool Global Gains recommendation. The Fool owns shares of Berkshire Hathaway. 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. The Motley Fool has a gold-plated disclosure policy.