I would recommend a very long weekend in Dublin. It's a beatiful time to go there and the weather is supposed to be superb.
I stayed on my last visit at the Brooks hotel which is located downtown with many sites in very short walking distance.
For a tour I would recommend Gallaway on the west side(it's 3 hours by train). and from there to the cliffs of moher - one the most beautiful sites I have ever seen!

enjoy