Let me suggest the Temple Bar.

Especially if you like oysters ... I don't, but my kids tell me they were the best they've ever had.

Oh yeah - they have Guinness on tap, too, I'm told.

The Shelboune is great but pricey. There are a couple of Clarions around that aren't bad at all - we stayed at the one at the IFS (near the O2) and had a great time. Rooms were huge and each of the corner suites had party decks. If I'm not mistaken, there's a free shuttle bus from the airport to the hotel.

Enjoy - it's a very lively city. We loved it.