The following commentary comes from an independent investor or market observer as part of TheStreet's guest contributor program, which is separate from the company's news coverage.NEW YORK ( TheStreet) -- You can't have an investment without a catalyst. The lack of a catalyst in a "cheap" stock keeps your money tied up in an investment that seems to have all the qualities you desire but suffers from depression that doesn't allow the stock to do anything but sit in place. Catalysts can come in the form of macro influences, restructurings, shareholder activism and management changes, just to name a few. The following are three companies with catalysts that provide the fuel necessary to reach their full potential: PostRock Energy Corp. ( PSTR): Given the enormous spike in natural-gas investments by all of the major oil/gas companies, it would be prudent to assume that there is a world of potential in small- to mid-cap natural-gas-related companies over the long-term. Aggressive investors should be looking for small-cap natural-gas stocks that have the potential for significant appreciation that will eventually make them attractive buyout targets for larger companies within the energy field. PostRock Energy deals almost exclusively in natural gas. The company has not taken part in the ascent that most other natural-gas companies have experienced over the past 12 months due primarily to some debt and litigation issues. During the second half of 2010, energy investor Thomas J. Edelman, through his newly formed fund White Deer Energy, injected a significant amount of capital into the company, allowing for a restructuring of debt and renegotiation of credit agreements. PSTR is generating a significant amount of cash flow from current operations. For 2011, the company is allocating $52 million toward capital spending, of which 100% will be funded with internal cash flow. Company management has been aggressive in drilling new wells and pursuing new leaseholds to further drive company growth. PostRock Energy owns thousands of miles of valuable pipeline for the transport of natural gas. As natural-gas growth occupies an increasing portion of energy infrastructure, the value of the pipeline will prove an increasingly attractive asset. The eventuality for PostRock Energy is that it may be acquired by a much larger company. In the meantime, it seems management is doing everything right for the stock price to appreciate. I currently own PSTR for managed accounts and have written an in-depth research report about the company. It's available on my Web site. GSI Group ( GSIG): GSI Group was on the verge of being plundered by incompetent management. Just a year ago, shareholders were wondering whether stockholders would see their shares dissolved as a result of a bankruptcy filing. An activist investor stepped in, formed an equity committee, fought a brilliant court battle and preserved shareholder value. GSIG survived and has appreciated more than 500% off its lows. Even during the bankruptcy battle, GSI Group continued to grow revenue, cash flow, product offerings and patent filings. The company has a diverse group of technology offerings ranging from semiconductors to laser technology. The most important factor investors are overlooking is that two years of performance, share appreciation and history is missing from the company as a result of the battle with former management. This has caused the shares to languish, remaining undervalued despite a complete transformation over the past 12 months. Debt and management issues have been resolved. The market is acting as if a black cloud is lingering. In this case, the market is wrong. Brigham Exploration ( BEXP): Brigham Exploration is a play on the Bakken shale. For those unfamiliar, I wrote a brief summary about Bakken a few months back. Estimates have varied widely about just how much oil/gas the shale contains. The one constant has been that oil/gas companies have been scrambling over the past few years to buy up acreage in the area. It is fair to assume that if estimates were exaggerated, these companies would be the first to play it cautiously. It has been quite the opposite, in fact. As technology has allowed these companies the luxury of recovering oil/gas in formations that would have previously proven impossible, the stampede to get a piece of the Bakken pie has only increased. When I look at Bakken plays, I see opportunity not only because of higher oil prices, but also in the potential rise in the value of land. The companies that own vast amounts of acreage in Bakken will see their share prices rise as land prices in the area continue to grow in value. Brigham Exploration owns nearly 400,000 acres in Bakken. The company has the liquidity to continue financing exploration and increased acreage in the region. As a result, BEXP has managed to grow production and revenue by more than 100% year over year. Crude oil prices will continue to climb over the long-term despite last week's sell-off. This will create support for oil/gas companies. The odds are heavily tilted toward a blow-off run in energy prices taking place sometime over the next several years. Trends in commodities rarely end with a whimper, much preferring a bang that leaves speculators' heads spinning. Crude oil will reach that point. Companies like Brigham Exploration will be prime beneficiaries. Disclosure: The writer is currently long PSTR.