Changingthepresent.org has a very interesting concept. It showcases charities, giving users and visitors the opportunity to donate money to their favorite cause. The donations are made to ImportantGifts, Inc., which redistributes the gift to the non-profits. The site offers a great way to search for charities to donate to, and the architecture makes it easy to find the exact cause you want to contribute to. I believe this is not the only social activism network, but it gets my vote.

From their about page: "For just a few dollars, you can provide a child with her first book; fund an hour of cancer research; protect an acre of the rainforest; or restore a blind person's sight with cataract surgery. ChangingThePresent.org offers a remarkably wide range of inspiring donation opportunities, so you're sure to find something that moves you."