1) The Constitution
2) EU law
3) Statute law (including statutory instruments)
4) Common Law & case law precedent.
1) Constitution - see www.constitution.ie for text and some official publications
2) EU law - see www.europa.eu (I'm not sure if that is the exact text but you can google) for EU laws
3) Statute law - see www.irishstatutebook.ie & www.oireachtas.ie
4) Case law & precents - see text books on Irish law or go to www.courts.ie and the judgements section for the most up to date judgements. www.bailii.org has a superior collection of caselaw as well as everything that is on courts.ie
You may also cite (refer to) jurists (academics) which form a persuasive (but not completely binding) opinion for some judges in particular case law (think Wylie for Land Law).
You would only mention that briefly however.
Also another persuasive source of Irish law is that of the European Court of Human rights, from which the European Human Rights Act 2006, draws from the European Convention of Human Rights (the basis for the European Ct. HR's decisions).
Finally, because we operate, at least broadly speaking, under the same system (common law system) as the UK, USA (minus two states), Australia, etc, judges often times are heavily influenced by judgments made by their common law counterparts in other jurisdictions. I'm aware that this comes under Johnny's post, but it might just be a little less obvious and therefore easy to omit!