You might want to check this out: Agenda For Justice . It's brand new, so the outcome and trajectory are unknown. But it looks good as a start-up.
And there's this one, too: Idealist . This site is particularly good if you're looking for a social justice-focused job.
The thing I know, and have come very begrudgingly to respect, is how organized and proactive the conservatives have been in marshalling their agenda through the courts, through the Congress, through the society. Progressives aren't going to do that -which is fine. We cherish diversity and process and freedom of inquiry. But surely we can talk to each other and learn from each other. Couldn't we develop an alternative vision for what society might look like and how we might create it?
I keep coming back to Margaret Mead and what has become the mission statement for my life:"Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it's the only thing that ever has."
Check these groups out and let me know what you think. Let me know if you find others that progressives might support.