The National Institute for Clincal Excellence (NICE) guidelines:
http://www.nice.org.uk/search/guidancesearchresults.jsp?keywords=hernia&searchType=guidance

Information from a good NHS website – NHS Choices:
http://www.nhs.uk/Conditions/Hernia/Pages/Introduction.aspx?url=Pages/what-is-it.aspx

Some more basic information:
http://www.surgical-tutor.org.uk/default-home.htm?system/abdomen/hernias.htm

British Hernia Society
http://www.british-hernia-society.org/

Melbourne Hernia Clinic
http://www.hernia.net.au/

A selection of articles on hernia in the British Medical Journal
http://www.bmj.com/cgi/search?fulltext=hernia&x=0&y=0