This programs allows you to create maps using a number of variables and export the map and/or its data. Includes basic instructions as you are creating a map and more detailed tutorials. Requires free registration.
GRASS GIS (Geographic Resources Analysis Support System)
Commonly referred to as GRASS, this is a Geographic Information System (GIS) used for geospatial data management and analysis, image processing, graphics/maps production, spatial modeling, and visualization. GRASS is an official project of the Open Source Geospatial Foundation (OSGeo).
gvSIG is an application designed for capturing, storing, handling, analyzing and deploying any kind of referenced geographic information in order to solve complex management and planning problems.
Quantum GIS (QGIS) is a user friendly Open Source Geographic Information System (GIS) licensed under the GNU General Public License. QGIS is an official project of the Open Source Geospatial Foundation (OSGeo). The program runs on Linux, Unix, Mac OSX, and Windows.
SAGA, short for "System for Automated Geoscientific Analyses," is a free, hybrid, cross-platform GIS software.
Also, be sure to check out the Open Source Geospatial Foundation's other projects.
GIS Data Sites By States
From the American Library Association. A list of GIS data sites from each state.
Many of the materials in this website are available for free download. You must create a GeoCommunity account to download data. Includes international data.
Provides access to over 400,000 (primarily geospatial) datasets from 172 agencies across the Federal government.
Geospatial Data Gateway (United States Department of Agriculture)
Source for environmental and natural resource data. Data can be downloaded as ESRI shapefiles for use in ArcGIS.
National Historic Geographic Information System (NHGIS)
Provides, free of charge, aggregate census data and GIS-compatible boundary files for the United States between 1790 and 2010. Free registration is required.
Geospatial and Attribute Links
A wide variety of links to websites with geospatial information. International focus.
CGIAR Consortium for Spatial Information
The Consortium for Spatial Information (CGIAR-CSI) is a group of fifteen international research centers that pioneered the application of Geographic Information Systems (GIS) and Remote Sensing (RS) for sustainable agricultural development.
Free GIS data
Free GIS data by state. Links to data from USGS, ESRI, EPA, Fish and Wildlife Wetlands, Agriculture's Soil conservation, FEMA flood and coastal barriers, Census Bureau, and assorted other links. You are directed to original data sites. You must have the appropriate GIS software and experience in order to utilize this data.
GeoCommons is the public community of GeoIQ users who are building an open repository of data and maps for the world. Allows searches or browsing by topic. Registration is free.