Global GIS DVD: Compiled by the USGS and the American Geological Institute; contains USGS and other public domain data, including global coverages at a nominal scale of 1:1 million in the following categories: Economic Structures, Environment, Gazeteers, Imagery, Land, Political, Rasters, Reference, Transportation, and Utilities. Several formats, mostly shapefiles or rasters.
VMAP Level 0 (formerly known as Digital Chart of the World)
From the US National Geospatial-Intelligence Agency (NGA), providing about the level of detail found on 1:1,000,000 charts. Worldwide layers are divided into 4 parts as below. The files are tarred and gzipped.
Natural Earth Public domain dataset, worldwide coverage at resolutations appropriate for 1:10m, 1:50m, and 1:110m scales.
Topical Geospatial Data
LandScanPopulation raster layers at 1 km resolution, for 2000 through to last year. Online viewer, or can access from GIS software as WMS images or WCS raster layers. Duke users only. NOTE forArcGIS 10.2.x users: When adding a WCS or WMS connection from Add Data...GIS Servers, to gain access you must enter a single space in both the username and password and check the “save password” box in the Add Data dialog.
Climate, Environment, Human Impact
UNEP GEO Data Portal From the UN Environment Programme. Files tagged "geospatial" will be rasters. Most other files will be data in tabular format with a locational attribute (country name, etc.).
FAO GeoNetworkLots of geospatial data from the Food and Agriculture Organization of the UN.
SEDAC (Socioeconomic Data and Applications Center) at CIESIN (Center for International Earth Science Information Network) at Columbia Univ.
Renewable Energy Data Explorer (REexplorer) Online mapping tool for visualizing energy-related map layers from selected non-US countries, most of which can be downloaded as GIS files.
CGIAR-CSI Consortium for Spatial Information includes links to detailed SRTM elevation data and several climate datasets.
Climate Hazards Center at UCSB Their CHIRPS dataset includes worldwide rainfall data rasters at .05-degree resolution covering back to 1981, at detailed time intervals. Compiled from both remote sensing as well as station data.
WorldClim - Global Climate Data Includes GIS raster layers in several resolutions representing global climate data normals based on 1950-2000 data. Also includes projections as well as paleoclimate reconstruction data.
Geology and Soils
World Geologic Maps Mostly small-scale GIS data from the USGS, many deriving from their Open File Report series.
Soil Geographic Databases Maintained by David G. Rossiter, who "attempts to catalogue all freely-downloadable primary soils information usable in a GIS either as "point" observations, polygon maps, or gridded maps ("rasters")."
Marineregions.org Includes data and links to data such as EEZ (Exclusive Economic Zone) boundaries, ecosystems, gazetteers of names, and bathymetry.