SeisSoft - Producers of projection and datum transform software. - http://www.connect.net/jbanta/
Decimaldegrees - Investigation of and experimentation with various GIS technologies, and the Internet. Latitude, longitude conversion and geocoding tools. - http://www.decimaldegrees.com
CoordTrans - Convert geographic coordinates between UTM, WGS84, NAD83, NAD27 and other national grids. - http://franson.biz/coordtrans
ZipMath - World database with latitude and longitude coordinates. Includes formula for calculating the distance between any two world cities. - http://www.zipmath.com/world.html