My favorite conference is Net Impact’s annual gathering, mostly because of the crowd — this weekend, about 2,500 people, most of them MBA students, undergrads and young professionals, gathered at University of Michigan’s Ross School of Business in Ann Arbor. These are the smart, passionate and committed business leaders of tomorrow. I’m proud to be on the board of Net Impact, a nonprofit that helps its members harness the power of business for the greater good.

So much programming is crammed into the two-day event that it can’t be captured in a single blog post or experienced by anyone, because dozens of sessions on different topics unfold simultaneously. But here are a few highlights:

What’s the future of recycling? It’s an unhappy fact that recycling rates haven’t moved up much since Earth Day. Yes, the original Earth Day, back in 1990. But innovative companies like TerraCycle, RecycleBank and Waste Management — yes, Waste Management, through a subsidiary called Greenopolis — are experimenting with clever and promising new ways to move the needle, by rewarding consumers for recycling.

I first wrote about RecycleBank in 2007. [See "Turning trash into cash" at Fortune.com] The company measures homeowners’ curbside recycling, and then rewards those who recycle with points that can be redeemed for stuff at more than 1,500 companies. “The idea of consumer behavior change is at the heart of our business,” said Ian Yolles, the chief marketing officer at RecycleBank, who previously worked at Nike and The Body Shop. The company is growing — it now operates in more than 300 communities in 26 states — and its investors include Coca-Cola, venture capitalists Kleiner Perkins and Generation Investment Management (the fund led by Al Gore and ex-Goldman partner David Blood). RecycleBank generates most its revenues by saving municipalities money (lower tipping fees, higher revenue streams from recycling) and taking a share of the savings.

TerraCycle has a more unusual model. It collects all kinds of hard-to-recycle stuff by mail — drink pouches, candy wrappers, plastic bags, wine corks, toothpaste containers — and then turns them into other things. “In 2011, you’ll see a playground made out of Capri Sun and Honest Kids drink pouches,” said Jo Opot, TerraCycle’s vice president of business development. Consumers who send trash get rewarded with donations to schools or charities, and they get the psychic satisfaction of knowing that something useful was made out of their garbage. You’d think that few people would bother to send their trash in the mail to New Jersey, Terracyle’s home base, but the company says 12 million people have participated, returning 1.8 billion items. The company gets paid by brands whose products it recovers, by manufacturers who buy its materials and by marketers who use its logo on finished products. There’s lots more about how this all works at the TerraCycle website.

For its part, Waste Management is rolling out Greenpolis, which offers interactive kiosks on streets, where people can recycle, as well as an online platform that offers rewards for recycling. In fact, all three of these companies want to get into the media business by engaging people on their websites. The Greenopolis website is packed with “green" content, and RecycleBank recently replaced its founding CEO, Ron Gonen, with Jonathan Hsu, who comes from the world of digital media.

Where’s the fortune at the base of the pyramid (BoP)? It’s been 12 years since Stu Hart and the late C.K. Prahalad began writing about the money that big companies can make by developing products and services for the world’s poorest people. The idea has instant appeal — help eradicate global poverty and make money, too!