If you are looking for real wood, as opposed to manufactured boards (MDF, chipboard, plywood, etc.), have a look at Lisnavagh Timer Project. They sell native Irish hardwoods and can do some (perhaps all?) of the preparation for you too. They list their current stock, and prices, on their website (
www.irishwoods.com) and I have found them to be very good to deal with. They have an ethical approach to sourcing wood too (they only sell wood from windblown trees, or trees that have had to be felled out of necessity), which appeals to me. Their site also has a fairly new discussion board, and people on that might be able to direct you too.
There are suppliers of hardwoods listed in the Golden Pages too, but some of them will only sell in large quantities, and I don't know if any of them will prepare the wood for you first.
If you are looking for manufactured board, and are based in or near Dublin, Woodworkers (
www.woodworkers.ie), in Terenure, are worth checking out. They'll give you prices over the phone, and they'll deliver (for an extra charge). I have made fitted shelving (8' high, about 4' wide) using 1-inch thick birch plywood from them before. They sell this in sheets of 8'x4' and will cut it for you too (they used to charge about £1 per cut). They don't sell much hardwood though, and their prices for hardwood were very high last time I checked.