Quantum GIS is a free (Open Source) program that that can be used to view, edit and print maps. Around the world it has an expanding user base of thousands of organisations.
DPCDB has used QGIS regularly since 2009 and found it to be invaluable... even more so because or its price!
You can get your free copy here or use this tutorial to explain how to get started.
In addition to free software, there is also free training.
To extend QGIS and make it even easier to use with Ordnance Survey maps, special plugins (extension programs) are being developed.