So, at first I didn't even want to mess with centerpieces. Then I found this idea:
http://2000dollarwedding.com/2008/10/socially-conscious-and-eco-friendly.html
Rebecca just sent a brilliant idea for centerpieces that are truly good for the Earth: gift baskets that would be donated to food banks after the wedding.
The idea came from reminiscing about her Bat Mitzvah centerpieces:
"I worked with my Mom to make food donation baskets! We painted the baskets in dusky rose and silver (sigh, my 13-year old color palette preference) filled them with canned food items, wrapped them in cellophane and ribbon, attached a note saying where the food was going, and voila!"
She continues:
"For a wedding, I'd probably go with something 'prettier' and stay away from non-eco friendly cellophane, but still. I was thinking maybe wrapping the cans and jars individually with pretty papers or simple ribbon, and maybe mixing them in with old tin-can vases for a similar stylistic impact (a la Style-for-Style). For shelters that accept fresh fruit, that's also a centerpiece option (not all do). Besides the charity impact and the waste reduction impact, using non-floral/non-perishable centerpieces would undoubtedly cut down on day-of stress about decor (flower shopping, transporting and arranging! ack!). For the less aesthetically inclined and DIY-impaired, I also found this charity that rents centerpieces in return for a charity donation."