NavigX is a Mac OS X application which converts between Ordnance Survey Grid References and Latitude/Longitude Coordinates.  It has the ability to import CSV files and perform a batch conversion on on the contents of the CSV file.  With configurable preferences, automatic update checking and an integral registration module, NavigX is everything that you need for Lat/Long and OS Grid conversions.

NavigX v1.0 requires Mac OS X 10.5 Leopard.