If you choose to run outside instead of using an electricity-driven treadmill, you're already doing your part to help the environment. You can do more though, with the help of the Brooks Green Silence running shoe ($100).
The heel cups are made with recycled CDs, and the laces, lining, and stitching are made with discarded plastic water bottles. The outer soles are made from recycled rubber, and the midsole is 100 percent biodegradable. All the soy-based dyes used are nontoxic, and the adhesives are water-based. The collar around the opening of the sneaker is stuffed with foam from old couches.