Here are some links to help you find accommodation in Ireland

Daft.ie – Has the most options for long and short term accommodation in Ireland
Rent.ie – Has many options for accommodation, including a section for students
Gumtree.ie – Has a few rental options and other useful classified listings
Jacobs Inn – Is an inn located in the Dublin city center and offers shared and private accommodation. Their Facebook Page usually has their best offers
Barnacles.ie – Is a hostel which offers discounted rates for long-term accommodation outside of the summer months
Anoige.ie – Is a Youth Hostel Association and offer many options all over Ireland