The biggest problem facing many parts of the world is not war, or HIV, or Bush invading. It's a lack of clean drinking water. I'm not going to list the nasty things that people can pick up through the water, but just about any disease you can think of is in it. This seems like the best solution I've seen. This Lifestraw filters out just about any nasty thing you could suck up (except a couple parasites - but their working on it). Fantastic.
It costs about 3 bucks which is too much for many of the people in nations who need it, but that seems to me to be the right price point for donations. One trip to the ATM can give 5 people clean drinking water for a year. Keep your eyes on this.
The Rational Moderate