I searched around on there, went down to Contact us, then Common Questions and this is what I found:
Is The Rainforest Site a nonprofit organization?
The Rainforest Site is not a nonprofit organization and cannot accept financial donations directly.
GreaterGood.org is the nonprofit foundation arm of The Rainforest Site and the GreaterGood Network. GreaterGood.org has applied for and is awaiting its 501(c)(3) status. When granted, that status will be retroactive to March 21, 2006.
How Do I Know This is Real?
There are a number of ways you can be assured that The Rainforest Site is for real.
Read the article on our suite of click-to-give sites, including The Rainforest Site, at Wikipedia.
Then they list 4 groups for you to contact (physical address, phone, email and web addresses) directly to make sure the group is legit: The Nature Conservancy, Rainforest Conservation Fund, World Land Trust - US, Friends of Calakmul.
They give all the contact info of these groups if you want to confirm this is a honest site.