Discount Tyres and Auto Service - in the Industrial Estate just beyond the National Aquatic Centre in Blanchardstown. Myself, the girlfriend and a friend have all had cars repaired / serviced there in the last fortnight and have found them to be very quick and considerably cheaper than the majority of other garages in Dublin - I got two tyres changed for €98, gf got clutch replaced for €200 and friend got battery replaced for €66.
They have a website with clearer directions and opening hours so feel free to Google them. Hope it helps!!