Where's the best open source map data?
I'm familiar with sqllite. Something like that would be useful for creating Geo Go. I can probably work with any map data, sqllite isn't required.
For now the map data should probably be extremely basic. Think something like minecraft map data but for the real Earth. Fancy stuff can come later on.
The best source of open source map data I can recommend is OpenStreetMap! I found a blog that offers derived OSM datasets, you are likely looking for the Land Polygons dataset.
The most important thing to consider is what map projection you are planning on using. Those listed as WGS84 will be using lat/long as the units, whereas the others listed as Mercator are using the Web Mercator projection perfect for building your own Google Maps, OSM map or any other major online mapping company (Bing, Yahoo, Apple etc.) All the files on this blog are available as shapefiles. If you need some GIS software for viewing these shapefiles, I highly recommend you use the latest version of Quantum GIS (QGIS) which can be found at http://qgis.org/en/site/
Just wanted to add that if you're looking for a minecraft style, you can check out this plugin for photoshop. A colleague of mine referred it to me and it looks pretty cool.