The national authorities of several countries have been producing safety material for many years, whilst the UK CAA publications are probably most relevant to operating helicopters safely in the UK, a lot of the other publications contain valuable safety information.

There are also several good sites with helicopter safety related information, some is anecdotal with no supporting evidence but well worth reading nonetheless.

UK CAA Publications
Safety Related Documents From Other Recognised Bodies.
UK CAA Offshore Publications
UK CAA Publications Not Specifically Safety