EcologyFund

So I won't go into great detail here, but check out EcologyFund.com. Its a cool site where you can donate to various organizations and you can also click on the buttons to save land for free. This works because every time you click on the save for free buttons, the sponsor orginizations donate the money to buy the land. Apparently if you check into the donor organizations, they double the donation. Whether or not that happens would require more research, but you should definitely check it out.