One of the great presentations at this year's Esri Internation User Conference came from Drs. Tim Schilling and Michele Adesir-Schilling. They talked about how GIS was used to help improve the quality of the coffee beans coming out of Rwanda. Higher quality coffee means higher prices for the farmer, which will help create a better quality of life.
A great article about their research can be found at http://allafrica.com/stories/201107210886.html.