The Temple Bar - a very touristy area, but probably what you want to see on your first holiday in Ireland. Pubs with awesome style, Irish beers, nice outdoors area to hang, and pretty areas to walk around too.
Colorful hostel in Killarney, Ireland (by philhaber) I absolutely love this place.) who runs the place is the best host I think I've ever come across. This is a must stay if you go to Ireland as far as I am concerned.