Demography

NHGIS provides, free of charge, aggregate census data and GIS-compatible boundary files for the United States between 1790 and 2012.

The US Census' TIGER Products are spatial extracts from the Census Bureau's MAF/TIGER database, containing features such as roads, railroads, rivers, as well as legal and statistical geographic areas

With the Metadata Explorer, you can search, browse, and download data from the FGDL, a mechanism for distributing spatial (GIS) data throughout the state of Florida

Enables everyone to find, use and share geographic data and maps. Easily create rich interactive visualizations to solve problems without any experience using traditional mapping tools.

"IPUMS-USA is a project dedicated to collecting and distributing United States census data. Its goals are to: Collect and preserve data and documentation, Harmonize data and Disseminate the data absolutely free!"

A free tool to download international GIS data by country

ESRI has tons of training materials for their product, ArcGIS. Here's a list of their free training resources.

Free desktop and web-based product for discovering, analyzing, using and sharing maps.

GIS Lounge is an information portal primarily relating to the field of geographic information systems. The purpose of this site is to provide introductory text for issues relating to GIS as well as interesting news items, tips, and resources for the geospatial field

A free and open source GIS.

A wiki of GIS software packages. Includes proprietary and open source packages.