UK resources

National Register of Archives
http://www.nationalarchives.gov.uk/nra/

UK Archives HUB
http://www.archiveshub.ac.uk

A2A (Access to Archives)
http://www.nationalarchives.gov.uk/a2a/

British Library
http://www.bl.uk

Wellcome Library (History of Medicine resources)
http://library.wellcome.ac.uk/