By now, everyone paying attention to the greening of corporate America knows about Walmart's sweeping sustainability programs. Big-box rival Best Buy has not been nearly as visible about its efforts to become more environmentally and socially responsible. But I recently visited Best Buy's headquarters in Richfield, Minnesota, on assignment for FORTUNE, and came away impressed with what the $40-billion a year company has been doing.

My story, headlined Best Buy Wants Your Electronic Junk, appears in the current issue (December 7) of the magazine, as the latest in a series on FORTUNE 500 companies. This one showcases a corporate responsibility leader, and we settled on Best Buy.

Why, you may wonder? Predominantly because Best Buy is a pioneer when it comes to electronics takeback, which is the focus of the story. In all probability, Best Buy has become America's biggest collector of electronic trash. You can bring back just about anything electric to any of the chain's 1,044 stores, and they will recycle it safely, sometimes for a small fee. (Read the story, and the fine print, before loading up the trunk of your car, please.) Takeback is an important and radical idea -- it's a pathway to a world where everything gets recycled and nothing goes to waste.

But Best Buy's doing lots more when it comes to corporate responsibility, and most of it seems tied to its business goals. The company would like to help customers make their homes smarter and greener -- part of a shift away from just selling boxes to providing services. It's taking responsibility for the way its suppliers treat their workers, by policing its supply chain. With a young workforce and young customers, its philanthropy is focused on teens.

More broadly, Best Buy and its new CEO, Brian Dunn, seem determined to create and preserve a listening, learning, open and transparent culture. Dunn told me:

One of my roles as CEO is to be the chief listener. I don't believe that the model is any longer that there are a few really smart people at the top of the pyramid that make all the strategic decisions. It is much more about being all around the enterprise, and looking for people with great ideas and passionate points of view that are anchored to the business and connected to things our customers care about.

Dunn's a likable guy -- an unpretentious straight shooter with a good sense of humor who rose up from the sales floor and never finished college. People at the company really seem to admire him. (Even those I met way off campus a few weeks later at the Net Impact conference.) I even did a little Tweeting with Brian (you can follow him at @BBYCEO) while fact-checking the story. He's by no means an imperial CEO.

The company isn't quite as transparent as it says it is, though. Its execs wouldn't talk in detail about the economics of recycling, or even say how many devices they've collected this year. Walmart's more willing to share what it has learned, in my experience.

Here's how the FORTUNE story begins:

At a Best Buy store in Roseville, Minn., the traffic in electronics travels a two-way street. Out the door go flat-screen TVs, netbooks, and iPhones. In comes junk -- and plenty of it: TVs that can't decode digital signals, outmoded desktop computers, even the occasional eight-track tape player or ham radio.

Since March, when Best Buy began offering free recycling of gadgets large and small, more than 25 million pounds of ISTB -- that's company lingo for in-store take-back -- has made its way to the company's 1,044 U.S. stores.

About 60 items a day arrive in Roseville, where Christine Cartwright, a store manager who rolled out the take-back program there, says she never expected to get into the recycling business when she joined the retailer. Dealing with all the unwanted stuff adds work, but it also brings an element of surprise to the job. "You never know what people will bring in," Cartwright says. "Some of these televisions ought to be in a museum."

So how, exactly, did Best Buy become America's biggest collector of electronic garbage? Where does it all end up? And can a big-box retailer turn all that trash into cash?

You can read the rest here.

GreenBiz.com Senior Writer Marc Gunther is a longtime journalist and speaker whose focus is business and sustainability. Marc maintains a blog at MarcGunther.com. You can follow him on Twitter @marcGunther.