A couple of websites I'd recommend:
NERA - National Employment Rights Authority
This website has been the subject of a media campaign lately. Definitely worth a look, although more relevant to permanent employment and fixed term contracts. Useful for employers and employees equally.
NRF - National Recruitment Federation
The NRF's brief is to establish standards and codes of practice for the Recruitment Industry in Ireland. In particular, if you are working with an agency, I would recommend familiarising yourself with the code of conduct.