Don't believe what your mom has been saying all your life—there is always a place for mud in the house, especially in the bedroom (kinky). The Mud Clock is a eco-friendly clock that requires no batteries, just a little dirt and water. Stick the clock powering components in the dirt and voila—the Mud Clock is functional. Toss some seeds in the dirt to grow some maize, or something. $20.
I don't know that I'd call it seriously eco-friendly. Although there's essentially no information on how it works on the product page, from the image it looks like nothing more than a potato (or lemon, or other vegetable) clock designed to go into dirt. So the power is coming from oxidation and reduction on the metal tabs they show sticking into the ground. Which, of course, will eventually corrode to the point where they need to be replaced, just like a battery. Somehow, I'm thinking that a way to extract electricity directly from growing plants would be met with slightly more fanfare than a $20 novelty item.
Summary: by a $10 potato clock, stick it in mud (free) and spend the other $10 on organic food or something else actually friendly to the environment.