Which de-icer is best environmentally?

Recently I wrote a short article, "Making Green Choices During the Holidays," for the Bethesda Green site. It contains some things you might have heard before -- real trees are better environmentally than artificial trees, LED holiday lights are better than incandescents -- but I also included some things I just learned, such as how the U.S. Postal Service now offers eco-friendly packaing. In fact, they are the first shipping company to use Cradle-to-Cradle certified packaging.

One thing I didn't cover in the story is eco-friendly de-icer/snow melt stuff. This became important during the last few days, thanks to the Blizzard of 2009.

Strosnider's in Bethesda usually has a variety of de-icing products, plus a flyer explaining the plusses and minuses of each -- including which ones are best for plants and pets (and thus the environment). This year they only had one kind for sale: Natural Alternative, from a local company in Frederick, Md. They claim it is safe for plants and grass, because it doesn't contain high amounts of calcium or sodium, even though it has some of both.

Meredith at B'More Green mentioned some other safe ice melters, and her colleague Tim thinks wood chips and sand (in moderation) are better.

What do you use? What's best environmentally?