McDermot's and McGann's in Doolin have been "discovered" and get rather full of Americans, but the music there is top notch (ask around to find banjo player Kevin Griffin). If you have any interest in nature, the Burren is a natural wonder -- perhaps one of the top two or three wildflower preserves in the world and May will be a good time to see it. Also from Doolin, hike the coast south towards the Cliffs of Moher and you'll see them completely without other tourists.

Enjoy, I'm jealous.