Earth Day 2010 has come and gone, but many companies are pursuing new environmentally sustainable initiatives all year long. Let's look at several interesting recent green developments that merit investors' attention.

The search for green energy
Search giant Google (Nasdaq: GOOG) made its name on the Internet, but it's now delving further into green energy initiatives that might mystify casual Google spectators. Big Goo recently coughed up $38.8 million to buy two wind farms in North Dakota, which together generate enough power for 55,000 homes.

This is even more interesting when you remember that late last year, Google formed a subsidiary called Google Energy. That offshoot allows the company to buy and sell electricity on the wholesale market, and it's probably linked to Google's vow to become a carbon-neutral company.

Like many massive high-tech companies, Google's business is power-intensive. Still, it's already making headway toward conducting its business in a greener fashion, including innovations like the 9,000 solar panels it's installed on its headquarters. Of course, Google might have other secret plans, too.

The greener Arches
The Golden Arches just got a little greener. Fast-food giant McDonald's (NYSE: MCD) has ramp up its sustainability efforts, according to Fast Company. It's got a green McDonald's in Cary, N.C., which includes LED light fixtures, VIP parking for hybrid cars, drought-tolerant plants, and electric-vehicle charging stations.

In addition, McDonald's has a sustainable fisheries program and has introduced a "low oil volume fryer" that allows the fast food giant to fry up the same amount of food using about 40% less oil.

McDonald's has also whipped up an environmental scorecard for its suppliers. This practice seems increasingly common, with Wal-Mart (NYSE: WMT) and Procter & Gamble (NYSE: PG) keeping similar tabs on the companies they buy from.

These initiatives from such large companies not only hold promise for increasing consumer goodwill, but may also eventually help companies run their businesses in a more efficient, less wasteful, and less expensive manner.

The end of plastic guilt
Thanks to a blog post in the CAPS community, I learned about a company that's making major headway in biodegradable plastic. Metabolix (NYSE: MBLX) recently received FDA approval for several of its Mirel bio-plastics products, for use in contact with food. Such applications would include plastic utensils, lids, and caps. They could also be used for freezing or boiling, and in microwave ovens. The compostable plastics are already being made through a joint venture with Archer Daniels Midland (NYSE: ADM), and they're turning up in gift cards and other applications.

The idea of being able to use biodegradable, plant-based plastics instead of petroleum-based ones is heartening indeed, given the disturbing amount of old-fashioned plastic stuffing landfills or amassing in the Great Pacific Garbage Patch.

What's next?
Sustainable initiatives not only make the world a cleaner, less wasteful place, but often help companies drive additional revenue, save money, or devise better operational processes. Given consumers' growing interest in sustainable living, companies that source their power or otherwise conduct business in eco-friendly ways could enjoy a significant boost to their public image. In the long run, that could benefit their shareholders as well.

Have you noticed any interesting green innovations among publicly traded companies recently? Want to call a company out for lame, half-hearted efforts to "greenwash" its image? Sound off in the comment box below.

Wal-Mart is a Motley Fool Inside Value selection. Google is a Rule Breakers pick. Procter & Gamble is an Income Investor choice. The Fool owns shares of Procter & Gamble. Try any of our Foolish newsletters free for 30 days.

Alyce Lomax does not own shares of any of the companies mentioned. The Fool has a disclosure policy.