I'm not a supporter of very many groups. Not really a joiner -- years of working in what should be the open-minded, disciplined-thinking setting of academia and other personality tendencies have made me very wary of "group-think," and individualistic and self-contained in many ways.
I tend to identify fatal flaws in the thinking of whatever groups I encounter, from the Sierra Club to the Tea Party.
But I've always been quite fond of Interfaith Power and Light. This group, which was part of the study for my PhD dissertation (on religious groups and climate mitigation), works to encourage members of the mainline religious denominations to consider climate change and energy problems.
Here's the latest news, whereby they attempt a petition drive to Congress and the President to say "enough is enough."