Coordinate Conversion,  Grid Conversion, and various Geographic Conversion Software

Auslig geographic calculation formulas> calculate distance between two lon/lat pairs, and etc.
CorpsCom (US Army Topographic Engineering Center) Transformation Software+ Other
Dr Math's Formula website - Formulas for many types of geographic and trigonometric computations
"Geocentric Datum of Australia - Technical Manual"> Lots of datum and other geodetic conversion formulas
Mentor Software> Coordinate Transformation and "Rubber Sheeting" Software
NimaMuse Coordinate Transformation Software
OSGB coordinate conversion to/from Lon/Lat using spread sheets