GISuser's Geospatial Data Resources.

Sponsored by ESRI. Access to worldwide data from governments and private publishers. Useful information on the start page - basic GIS information, map types of high interest (e.g. TIGER Census maps).

Special interest and thematic groupings make this easy to navigate. A one-stop shop!

The data sets are being delivered in industry-standard shapefile format (compatible with Arc- GIS products) derived from the
 public product created from the Census Bureau's TIGER^® (Topologically Integrated Geographic Encoding and Referencing) data base of geographic information.

The Census TIGER database contains spatial information on physical land form features, political boundaries, and census boundaries with their attributes, such as their location in latitude and longitude, the name, the type of feature, address ranges for most streets, the geographic relationship to other features, and other related information.

An up-to-date and maintained base of quality geospatial data for all of Canada to provide the reference and context for a broad variety of thematic data for government, business, and personal applications.

Mostly On-Line and Mostly Free U.S. Geospatial and Attribute Data - Second Edition

National Atlas raw data come from many different Federal agencies and these agencies are often the best sources for more detailed information. National Atlas Map Maker includes links to sites where you can view detailed aerial photographs and large-scale topographic maps.

The National Map Seamless Server is the ultimate location to explore and retrieve geospatial data from the  U.S. Geological Survey (USGS) and the EROS Data Center (EDC). An approach is to provide free downloads of national base layers, as well as other geospatial data layers. These layers are divided into framework categories: Places, Structures,Transportation, Boundaries, Hydrography, Orthoimagery, Land Cover, and  Elevation.

This site provides data on international trade, national accounts, energy, industry, environment, transport and demographic and social statistics gathered from many national and international sources. The FREE to the public UNCDB (United Nations Common Database) is especially impressive with data from up to 50+ years ago.

Be sure to dig deeper in the search engine - use the Advanced Geography Search to find smaller census units such as tracts, block groups by using an address.

http://factfinder.census.gov/servlet/AdvGeoSearchByListServlet?

Demographic, economic, socioeconomic and health statistics by country or regional groupings. Also links to other international data portals.

to convert latitude and longitude from NAD 27 to NAD 83 or from NAD 83 to NAD 27.

GPS Visualizer is a free, easy-to-use online utility that creates maps and profiles from GPS data (tracks and waypoints), street addresses, or simple coordinates.
Additional utilities:

• geocode multiple address and tabular data
• Import GPS data file or plain text data and output KML file viewable in Google Earth applications
• Create overlays for use in Google Earth