There are really great websites that locals and tourists alike use.
www.visitdublin.com the official Dublin Tourism Web site
www.thingstodo.ie provides a searchable database for Dublin and all of Ireland
www.dublintourist.com provides a directory of Dublin attractions
www.hidden-dublin.com has a humorous section to make planning visits fun.
Renaissance Card has super deals on clubbing, drinks, food, activities and more!
Look Around Ireland shows 360 video views of Dublin and Ireland.
Obviously, TripAdvisor's Dublin Pages are full of information by travelers for travelers.