Somewhat unfamiliar to me is the Natural Earth project, providing free raster and vector data of administrative borders, disputed areas, populated places, urban polygons and water boundaries in addition to much more. Great for updated maps. For historical shapefiles. Check my post on the cShapes dataset. From their website: “We developed Natural Earth as a [...]

CIESIN and Yale University has released the 2010 data of their data set on environmental performance index. GisIntersect has created a map from the dataset, available here Click the map for full size:

Nils Weidmann at Princeton University and Kristian Skrede Gleditsch at the University of Essex has constructed this historical border dataset. The cShapes package includes all state border changes from 1946 and onward. It provides an excellent dataset to visualize border changes, in addition to construct historical data. The dataset is available both as an R [...]

ArcGIS online resources center provides some very interesting basemaps for free. If you only need some background maps to visualize your information on, then this is a good solution. The service includes both basemaps, reference maps and elevation maps. There is a high degree of US maps, but still lots of valuable and time saving [...]