Once upon a time, a company's "green" efforts were often esoteric and token bets conducted primarily to burnish a reputation as a corporate citizen while making little actual difference to the world, and often actually harming the bottom line.

But a new Newsweek ranking of the greenest big companies in America shows that economic benefits and ecological ones are not mutually exclusive. In fact, the green rankings might well provide a key indicator of which companies are the most innovative and forward-thinking, the ones that are, for example, getting ahead of a potential federally mandated cap-and-trade system for reducing carbon emissions. And as global pressure increases for more effective environmental stewardship, established green policies will provide a competitive advantage. As an added bonus, it feels better to invest in companies that are trying to limit the trash they dump into the world.

In the same issue of the news magazine, British Prime Minister Gordon Brown wrote of countries' green positioning in the run-up to the U.N. climate change summit in Copenhagen, but he also could have been talking about corporations when he said, "The economies that embrace the green revolution earliest will reap the greatest rewards."

In short, environmental sustainability is smart business. Take a look at some of the winners.

Hewlett-Packard (NYSE:HPQ) earned the top spot in the Newsweek rankings because of its programs to reduce greenhouse gas emissions throughout its supply chain. HP backs innovative and earth-smart initiatives, such as its electronic products recycling program, in which it pays customers to ship back obsolete machines that has allowed the company to reclaim 1.7 billion pounds of waste over the past decade.

Adobe Systems (NASDAQ:ADBE) came it at number 16 on Newsweek's list, in large part for its goal of offsetting 100% of its carbon emissions for fiscal year 2009, and for redesigning its software packaging to include recyclable and sustainably sourced cardboard and significantly less dye. The technology company also is a recommendation in The Motley Fool's Stock Advisor newsletter service and is at the forefront of the cloud computing wave, even more so after committing $1.8 billion to acquire Omniture (NASDAQ:OMTR), a combination that could bring highly regarded measurement and analytics tools to developers and owners of cloud-computing software.

Staples (NASDAQ:SPLS) has been increasing the use of recycled content in the paper it sells and purchasing paper products from well-managed forests since 2002. That and other efforts -- such as retrofitting stores with energy-efficient lighting -- earned the company the 20th slot on the list. The dominant office retailer, also a Stock Advisor recommendation, continues to post industry-leading margins, but current valuations make it only a hold for now.

Intel (NASDAQ:INTC) buys renewable energy for nearly half of its energy use and is the largest corporate purchaser of renewable energy in the country. The company also works to reduce energy consumption in its chips, which not only makes them more environmentally friendly, but also helps Intel's customers reduce costs.

Marathon Oil (NYSE:MRO), a five-star stock in CAPS, shows that no industry is barred from green innovation. "Oil companies are generally not poster children for the environment," reported Newsweek. "Marathon stands out in its industry, however, by generally avoiding the controversies and enforcement actions plaguing other oil giants ... [It] also has solid management systems and aggressive GHG emissions reduction programs in place."

Even lower-ranked companies, and those not exactly known for their commitment to addressing environmental concerns, are starting to get in the green act. ExxonMobil (NYSE:XOM) ranked a not-particularly surprising 395th out of the country's 500 largest companies, but Forbes named it the Green Company of the Year. The company has earned kudos for its plan to grow green algae to fuel cars, and Forbes raved about its progress in liquid natural gas, "the answer to green-energy low-carbon concerns," according to Neil Duffin, president of ExxonMobil's project development company.

It seems unlikely to me that the company responsible for -- and long indifferent to -- the ecological disaster of the Valdez oil spill would be seeking such green solutions if they weren't tied directly to a different kind of green.

Are all green companies great investments? Of course not. But if you like investing in great companies that are forward-thinking, innovative, and maybe even outstanding corporate citizens, Motley Fool Stock Advisor can help. Since inception in 2002, advisors Tom and David Gardner's recommendations have returned 49% versus 0% for the S&P's 500. A no-commitment free trial gives you full access to all of their top recommendations right now. Simply click here.

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You'll have to excuse Roger Friedman's concern for the environment. Before he joined the Fool, he spent two years hugging pandas as online managing editor of World Wildlife Fund. He owns none of the companies mentioned, but he appreciates their green efforts. Adobe and Staples are Stock Advisor recommendations. Intel is an Inside Value pick. The Motley Fool has a disclosure policy.