Does anyone know of a good program for converting coordinates between different datums. I'm currently using GeoPosCalc which is pretty good but missing one feature I need.

Ideally I'm looking for a program that can handle having the northing in one datum and the easting in another and then spitting out the answer in a datum or format of my choosing.

All the programs I've found so far need to have both lat and lon in the same datum.

Cheers.