The Field Guide to Humanitarian Mapping.

A free publication to help aid organizations use geospatial tools and methods in their work in emergencies. It’s published by MapAction, an NGO that works specifically on mapping for humanitarian emergencies, deploying volunteer GIS professionals around the globe.

See also Mapping for Advocacy, a collection of 10 case studies, and Maps for Advocacy a more general introduction to geographical mapping techniques for NGOs. Both booklets are free to download. While not specifically oriented for NGOs, Making Maps is an also excellent general primer. The Making Maps blog hosts some interesting discussion as well.