Give Earth a Hand - http://www.giveearthahand.com - is a social network supporting non-profit projects worldwide which work towards helping our planet.

We are currently looking for new members to sign up to help spread the word (it's for free) and if they like the idea, they can sign up for 2 Euros and join the 'Earth Chain', which will allow 1.8 million people to support these non-profit projects. Each member receives an individual figure in Google Maps showing who they are and it links to your profile.

Read about Asi Sharabi's call for ideas and a good suggestion from Seth Godin in the blog of Dave Weinberger (a co-author of the Cluetrain Manifesto, a must read for those interested in using the web to effect change).