Went there this past summer with the wife for 48 hours.

Take the train/light rail to Howth, which is about a 30 minute ride. It allows you to see the coast without having to drive across the country. There's an awesome four mile mountain hike and a great few seafood restaurants in the village.

Also, if you are into craft beer, that scene is beginning to ramp up. There's a place called Dublin Beer Market that has approximately 30 beers on tap, mainly from Ireland.

I encourage you to check out Brazen Head, which is the oldest pub in Dublin. It's a little away from other tourist attractions, but I think the history and food are awesome.

Finally, a lot of people like the Temple Bar area. Depending on your age, you may feel the same. We are in our early 30s and felt like it was something we would have enjoyed 10 years earlier. Needless to say we did avoid it bc I'm not into huge crowds and loud scenes anymore.

Also, take the light rail in from the airport as opposed to a taxi. You'll save about $50.

Have fun, it's a really cool place and you can fit a ton in over a couple of days. We walked pretty much everywhere bc the city is fairly easy to navigate. And the Irish love their Americans or they at least loved us.