(I am part Irish but I live in the UK
.)
Kilmainham Gaol and the Guinness place are both good.
U2 filmed a music video in the Gaol, and also I'm not sure but were they part of the Amnesty thing there? I know the Corrs were... Can't remember if U2 were aswell.
It's definately worth a visit anyway.
The Guinness place is also v.cool. The Gravity bar there, is where the aftershow party of some Hot Press awards were a couple years ago.
You get this (free) cool guinness paperwheight thing and a free pint of guinness.
You must go to The Clarence Hotel too! The do The Best chips EVER there!!!
Captain Americas (restaurant - bit like TGI's/Ruby Tuesdays) is also very cool as they have loads of U2 stuff all over the place. (I took pics of this which I could upload for you if you want?)
Also there's a plaque of U2, on the wall somewhere, I think by TGI's outside the St Stephens Green shopping center. Could be wrong about where it is, these plaques are all over Dublin, for different artists. It's called the Dublin Rock and Roll walk of Fame (I think!!!).
Hmm, dunno what else... That's just a few things I did when I went to Dublin last year. I was only there for 3 days.
There's a website called the U2 stalkers guide to Dublin... Not sure if it still exists...