Alfred Leick's home page with numerous articles that are accessable addressing, mainly, GPS information
Australian Surveying and Land Information Group Geodesy home page with links to GPS and other geodesy topics, including calculation methods with MS Excel spreadsheet calculations.
Datums, Coordinates and Transformation
Global Positioning System
Geodetic Reference System 1980 by Helmut Moritz
Earth Orientation Department U.S. Naval Observatory
International Earth Rotation Service (IERS) Central Bureau.
Time Service Department U.S. Naval Observatory.
Ordnance Survey, United Kingdom (formerly the Directorate of Overseas Surveys). There is a short history of the survey at this site