This is so convenient - right across from Trinity College and my hotel (the Westin) - good knowledge. They preview the CDs and the woman behind the counter was very helpful and patient in playing CDs for me in advance of purchase.
If you like the music -- or you're curious about the music, or you want to know where to find a good session at a local pub -- be sure to visit Claddagh Records. The staff are great, and full of recommendations. Just be careful not to walk out with more music than you can technically afford!