New/ second hand?
contemporary/ modern/ antique style?
If you are after new contemporary furniture (and alot of it)- personally I'd take a trip up to Belfast. There's a shop called Creations that does alot of lovely furniture plus they deliver to the Republic as well.
My wife and I had seen a lovely dining set, sofa and 2 bedroom sets in Harvey Norman and Diamond Living. We were delighted to find the same ranges of what we had intended to buy in Creations, and bought it all there and saved ourselves about 20% of the cost including the delivery charge.
For one bits of stylish furniture, I love Habitat.