Kiva

Kiva combines microfinance with social networking. It's a platform which lets you lend small amounts to poor entrepreneurs to help kick-start their business. It's a combination of microfinance and social networking, allowing you to connect to your recipients.

Kiva is famous as the poster-child of social entrepreneurship, and one of the biggest breakthroughs in the field. Through micro-lending, you can "recycle" your contributions (they're loans, not donations); and you're "teaching a man to fish" by aiding in economic development, rather than through band-aid donations.