There are numerous sources of information on magnetism on the web today. We have listed a few sites that we know about. The Great Magnet, the Earth - A fantastic NASA site about Earth's magnetsim begining with the work of William Gilbert in 1600. U.S. Gazetteer Site hosted by the U.S. Census Bureau where you can find information on cities within the U.S. searching on city name or postal code.
Information includes the latitude and longitude .
National Space Science Data Center, NASA This location has software available to generate geomagnetic coordinates for geographic locations. The WWW Virtual Library - Geophysics Links to resources on the web. Chris M. Goulet's Frequently Asked Questions concerning magnetic declination. A worthwhile site for the content if you can manage to read it. Follow the Western Washington University's construction of a magnetic field free room Images of the Earths Magnetic Field for D, H, Z, I, and F for selected periods from 1900 - present.