Not a nightlife spot, but a listings magazine which is free everywhere called the Event Guide. Practically everything that happens in Dublin is listed here from Gigs to clubs to art exhibitions to public talks. Check it out.
A lot of visitors who come to dublin tend to do all the touristy stuff during the day and then head out at night for one glass of guinness before calling it a day. If that's your bag, cool, but although Dublin is getting more and more expensive you really have to catch a flavour of the Irish at play before going home.
these geezers here in de photo are called the red settaz. you'll see them in listings all the time. they normally just play decent events so you're safe enough there.