For available datasets, see Atlas
Geography being an import part of most school curricula there are a few Open Content projects that could be implemented. There already exist two open content projects that could be adapted for the OLPC.
 Specific projects
Openstreetmap.org is a project to create free and open licensed maps of the world. The website is similar to Google Maps on the face of it, but the map is editable in a wiki-like approach, and OpenStreetMap is a not-for-profit mass collaboration which releases all underlying vector data for free. There many different software's for viewing maps, including interesting offline and highly compact vector-based options. For editing, the primary options are an an online flash editor, which sadly doesn't work well with Gnash, or a java desktop application JOSM. JOSM works on openjdk. It also has some offline editing capability (save changes to file and upload later), as such it is the editor of choice for the Humantarian OpenStreetMap Team who are working on and promoting mapping in the developing world. They also develop learnosm.org training materials.