ReplyforAll is a free service that turns every e-mail into an opportunity to raise funds for your charity or cause of choice. Users sign up at the ReplyforAll site, select their cause or charity and upload a custom ReplyforAll signature.
The ReplyforAll signature includes a tally of how much money you've raised, your preferred cause and a fundraiser's ad. That ad is the source of the funds that go to your charity of choice. It's a great way to passively donate to charity without interrupting your regular routine.