Ok, there are obvious favourites that I love like the Gas Building, Dept of Enterprise, Sunlight, plus Georgian & Gandon stuff of course... I'll skip all those ones.
My other picks are (in no particular order)... corner of Dame St & Grafton St (Fox's), Restaurant in UCD, Post Office off Suffolk St (are they v. boring choices?).
Also a building I don't know the name or purpose of on the North Quays, and in fact can't remember which Quay, but next time I pass it I'll take note & post again. Also on Westmoreland St. & Eden Quay there are a couple of gorgeous office fronts. The West. St. one is I think an insurers or solicitors, it's on the West side just beyond Bank of Ireland, the Eden one is something to do with shipping I think. Ok I know that's not much help, I'll repost those vague ones!