Visitors and sponsors of the therainforestsite.com are saving around 600 acres of rainforest a month. You can help and it only takes a minute. Go to therainforestsite.com every day and click the button. The clicks are counted and used by the site to get donations from sponsors.
Another no-cost place to generate a donation to save the rain forest is rainforest.care2.com. It works the same way: one click per computer per day, sponsors pay for the number of clicks and the money goes to conserve land.