Credoaction.com / Stay away from this one
CREDO Action is one of the many online petition sites that you'll see passed around facebook and e-mail. I signed at least one petition through them, and they began sending me regular e-mails, as most online petition sites do. (I'm also on the change.org and avaaz.org mailing lists.)
I do not like CREDO. For one, they are extremely liberally biased (and that's saying something for me, as a social liberal). I was disturbed they were collecting money to "fight against the tea party." There are so many social injustices in the world, why should they raise money to quell someone's freedom of speech?
For two, they use un-scientific rhetoric. I received several campaigns against "pink slime" from them. While it's true the meat product they're referring to is low quality and fatty, slinging slurs like "pink slime" in the face of scientific testing is in itself disgusting and disgraceful. A bad product will be obviously bad, without giving it ridiculous labels. I have seen the way the "toilet to tap" branding was used to destroy a perfectly valid scientific treatment of water. It is a distasteful way to run a campaign.