National Atlas - Environmental, demographic, transportation, boundary raw data used for NationalAtlas.gov
GIS Data Depot - U.S. and some international geospatial data (Requires login)
Starting the Hunt - By U.S. state. Includes links to attribute data as well as geospatial data
National Historical GIS - Historical U.S. Census data (1790-2000)
Census 2000 TIGER/Line Data - From ESRI
Census Bureau Maps - U.S. Census Bureau. Includes up-to-date boundary files
CloudMade - Detailed political boundary maps of countries and many more.
Historical GIS clearing house - List of many external, international GIS data sources.
Natural Earth - Public domain map dataset available at 1:10m, 1:50m, and 1:110 million scales
Stanford University: Websites for Digital GIS data - Links to many useful GIS data sites
How to find coordinates on Google Maps 1 - Short Java script method
How to find coordinates on Google Maps 2 - Google Maps Add-on