Day 19 of the Advent Calendar brings a link to that most useful of all online catalogues for British genealogy: the National Archive. You can download some documents for very little cost – others you can order copies of. The catalogue also incorporates basic details of resources and documents held in Local Records Offices and archives: very useful indeed for a one-stop search.
The latest version of the catalogue is known as “Discovery”- you can find it here:
http://discovery.nationalarchives.gov.uk/