When you think of public companies, what immediately comes to mind? Sure, there are the big, bad conglomerates, the brands that everyone knows, the big technology firms, the retailers large and small, industrial and transportation companies, and so on and so forth. But with 6,000 companies listed on the three major exchanges, you have the potential for an incredibly diverse array of businesses, models, and services provided -- any of which could be a potential investment.

The idea for this article came from two places: one is a total prejudice; the second, a fascination. The prejudice is this: I have an innate distrust of companies that do not produce or market something tangible. The banks, investment banks, consulting firms, and the like -- I have an extraordinarily difficult time trusting them. It's a prejudice, pure and simple, but two concepts keep me cautious.

The first is Warren Buffett's simple exhortation that you should look for businesses that can be run by monkeys, because eventually they will be. The second is a story from John Train's The Money Masters, in which legendary investor Paul Cabot noted with contempt that a bank had lowered its dividend while raising its salaries. He told the bank president that the company shouldn't be rewarding its "boys" while making shareholders suffer for poor performance -- to which the president responded, "We haven't got anything except our boys."

Like I said, it's a prejudice. But I see what can happen with a BearingPoint (NYSE:BE), where compensation costs spiral while shareholders suffer, or at an FTI Consulting (NYSE:FCN), which lost more than 40% of its value on news that several key employees were bolting. And then I resolve to make sure with service firms that my margins of safety in the investment are huge, because in the business themselves, there doesn't seem to be much in the way of safety.

The task for investors of determining what is sustainable for these companies is difficult, and there are minimal fixed assets to fall back on. Of course, in some cases, like Jacobs Engineering (NYSE:JEC), you have service firms that can become quite inexpensive -- most likely because they're misunderstood by the likes of, well, me for one.

I also have a fascination with the bizarre. Sure, we all know that Tiffany (NYSE:TIF) sells jewelry, McDonald's (NYSE:MCD) sells hamburgers, and so on. But what to make of companies that sell, for example, tombstones? Or golf club shafts? Or licorice extract? Can you name a company off the top of your head that sells any of these? They exist. Better yet -- they're publicly traded. And because these industries are out of the way, an investor who focuses on them is looking in places where opportunity isn't necessarily picked clean.

I call these companies "freaks" in the classic carnival sense -- there isn't necessarily anything negative about it -- they're just way off the beaten path, and some of them are interesting companies. Think of it this way -- if General Electric (NYSE:GE) is America, these companies are the equivalent of Nauru, Bhutan, Papua New Guinea, or Liechtenstein. Obscure, out of the way, but not necessarily poor.

Here, then, is the gallery.

Here comes Santa's super sleigh
In the movie About a Boy, Hugh Grant's character doesn't have to work because he lives off the royalties of an annoying holiday carol his dad had penned 50 years before. Royalty companies are like that -- Qualcomm (NASDAQ:QCOM) may be the best-known royalty company, but Motley Fool Stock Advisor selection ARM Holdings (NASDAQ:ARMHY) and InterDigital (NASDAQ:IDCC) are more pure plays than the big Q.

These companies have an installed portfolio, and anyone who wants to use their technologies pays a toll. Some have described these companies as the closest thing we have to publicly traded law firms. Were it not for the need and desire to develop new technology patents, these guys could be sitting on a beach somewhere waiting for their checks to show up. (Of course, none of these companies really qualifies as being off the beaten path.)

There are some corporations that have such bizarre combinations of business that you just can't believe that it happened this way on purpose. There is, of course, insurance/furniture/candy/framing/manufactured housing/shoe/brick/paint/vacuum cleaner/cutlery-selling Berkshire Hathaway (NYSE:BRK.A) (NYSE:BRK.B), but Warren Buffett has shown that he knows a thing or two about capital allocation.

There are also plenty of other brand-management companies like Brown-Forman (NYSE:BFB) and Constellation Brands (NYSE:STZ). But what about Middleton Doll (NASDAQ:DOLL)? Middleton Doll produces Lee Middleton collectible dolls, but the company also operates as a real estate investment trust, providing leasing services and loans to small businesses. Or how about Alexander & Baldwin (NASDAQ:ALEX)? I found Alexander & Baldwin interesting due to the enormous acreage of Hawaiian land that it has held for decades and that is carried on its balance sheet at its acquisition price. But this company is a shipping and container maintenance firm that produces electricity, molasses, and sugar, as well as develops real estate.

Pizza in a cup
These are firms that are in the mold of one of Peter Lynch's favorite investments: a company that made sausage casings. These are businesses that most people never think of at all, much less as potential investments. Several years ago, I profiled a few companies with businesses that sit well outside public consciousness, including Stepan (NYSE:SCL), an intermediate chemical company, and USEC (NYSE:USU), a uranium enrichment company. More recently, we discussed the Potash Company of Saskatchewan (NYSE:POT), which mines, if you can believe it, potash.

There are plenty more obscure businesses out there, though. How about M&F Worldwide (NYSE:MFW), which produces licorice flavoring for food, tobacco, and pharmaceutical companies? Or Rock of Ages (NASDAQ:ROAC), which retails granite quarried from its location in Vermont for use as tombstones? Or Gallery of History (NASDAQ:HIST), which markets historical documents and autographs? If these pursuits are not quite what you're looking for, then perhaps graphite golf shaft maker Aldila (NASDAQ:ALDA) fits the bill. This past year I held off buying Aldila because it moved from $2 to $3 while I was analyzing it. Now it's at $15 and probably overvalued. (But what do I know? I sucked my thumb while waiting for it to come back when it was at $3.) Sticking with the golf theme, there's Natural Golf (AMEX:NAX), which offers golf clubs, golf schools, and instructional devices to help people improve their games using its proprietary methods.

All of this goes to say that if there is something -- anything -- out there that you're interested in, there is more than likely a company that you can invest in that's doing it. Moreover, there are other companies that are running businesses in areas that most people simply don't think about. And while some of them are well-deserving in their obscurity, among them -- like an Aldila -- are some gems in places where most people don't think to look. So the next time you see a freak, don't scream or run away. It might offer you the chance at some outsized returns.

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Fool contributor Bill Mann holds shares in Berkshire Hathaway and McDonald's. He's owned a few strange companies, too. None mentioned here. The Motley Fool is investors writing for investors.