I was really impressed with the Guinness Storehouse. It was all laid out in a really interesting way and for something which if done in the wrong way could be a little on the boring side - it was actually a really engaging and informative experience. I would definitely recommend it as a place to visit in Dublin.
I would highly recomment the traditional Irish Music pub crawl. The musicians are really friendly and down to earth and help you to understand the "real" non-touristy Dublin. They teach you about traditional music and the instruments used. They sing traditional sings which range from soft and moving love songs to some more light hearted and cheeky stories told through song. Very authentic and very Irish. I would definitely recommend this to anyone who is visiting Dublin ot Ireland for the first time or for a short time and who wants to get a feel of what the city / country is all about.