Parts of the world will become virtualized as time and people arise to tackle them. If you are working on any particular location and are willing to be listed here, please let us know.
A great deal of data for the USA can be downloaded or ordered from the USGS (mostly from their websites EarthExplorer and National Map, although not all USGS data is free online).


the University of Florida Geoplan
Center gathers Federal, State, and local GIS data and Imagery and distributes
it for "free" (non-redistributable) as part of the
Florida Geographic Data Library (FGDL)