The Cliffs of Moher are touristy as all hell, but stunningly beautiful. And driving through the countryside to get there is very pretty.
www.cliffsofmoher.ie/
Galway was probably my favourite place in Ireland. Lovely little town on the west coast.
If you're wanting to party it up in Dublin - which is a hoot - try and make some local friends who will take you to pubs/clubs outside the Temple Bar district (pricy tourist bar central - English hooligans coming in for the weekend to fight each other). The most fun I had was at little pubs scattered around various parts of the city. However, I can recall none of their names.
Messers Maguire was a good spot, right downtown. That's all I can remember though (I went there a good few times).
Trinity College is a beautiful campus to explore.