FightHunger.org is a project from the UN World Food Program, which aims to help to end child hunger in the world by 2015. They hold an annual worldwide demonstration across the globe called Walk the World.
I've been working with them as a Drupal consultant for several months. The web site is built on Drupal and is used for the organization and follow up of campaigns and events around the world.
Besides an online store implemented using eCommerce package, there are a lot of custom developments done for this site, like a multi-currency donation module with payment system integration, and the web tool used for the Walk The World campaigns.