Top Ten Enterprise Customers

4. Walmart

If this cheap company can go green, so can you. The massive retailer Walmart began a push into green technology in 2005 as a way to cut its overhead costs. It worked. Removing light bulbs from coke machines saved $1 million alone. Another $10 million got saved by better recycling practices. The sheer scale of Walmart suddenly made it one of the biggest customers (and experimenters) with technologies like LED lighting, solar lighting, and fuel-cell powered forklifts.

In 2008, it started thinking outward. It told suppliers that they had to increase their energy efficiency by 25 percent by late 2010 and said it would sell only Energy Star-rated air conditioners. Flat panel TVs would have to become 30 percent more energy efficient.

"If we achieved our 25 percent goal just in the U.S. we would save enough electricity to power 3 million homes per year or the equivalent of 10 million barrels of oil," said then CEO Lee Scott in a speech to employees at the time.

Walmart's diktats do not always go fulfilled. Carrots and sticks to get suppliers to adopt RFID tags fell flat. But, unlike the RFID push, Walmart isn't the only one benefitting here. By cutting energy, suppliers will be able to streamline their own costs and prep in advance any carbon legislation proposed by President Obama.

The green scope expands by the year. The latest directives are to reduce plastic bag waste by one third and have suppliers cut packaging by 5 percent by 2013. Wastewater treatment plants are being added to all of the stores in Mexico.

Oh, and it's good business. The company is one of the biggest retailers of energy-efficient bulbs and heavily touts products like recycled plastic hangers. Honorable mention: the much smaller, but hipper Target.