musicmaker and musician inc are the two main ones, a few minutes off grafton street (south of the river). (they have websites, you could google them i guess, i don't know them offhand).
there are a load of other ones, i guess, and i'm not a native, so there are probably some i've missed. EDIT: those two are probably the only two worth going out of your way to, and to be honest since you're from england you probably won't be super-impressed by those either. You won't be impressed by irish prices either... :o
i normally just check out the yellow pages when i want to find guitar shops(or golden pages as i think they're called down south)... you can access that online.
