If you have to exercise indoors (where "have to" is defined as "want to because it's been so cold this winter that you feel like you're going to die each time you put a toe outdoors but you are also simultaneously repulsed by your own slug-like visage in the mirror") and you know that I've already dissed the treadmill in terms of planet green-ness, what are you going to do? Hey, how about spinning?
Spin class, also known as riding a stationary bike while an instructor yells at you to go faster and increase your resistance, uses no electricity (other than the lights and sound system). It's pretty fun too.
I think it's still not as great for the planet as cycling outdoors, but some days, you need to sweat, it's freezing out, and yoga just isn't going to cut it. Spin class is a very planet-green and pocket-green option (using all of Tony's arguments in favor of indoor exercise presented in the treadmill post).
I am also wondering, just because I'm crazy, if it would be possible to hook up a generator to the back of the spin bike to capture the energy created by the spinning. Why yes, crazy lady, someone has done this. I smell a physics project. Tony?
Pocket: 6, Planet: 12, Win-win: 29