Collins Bird Guide (Mullarney, Svensson, Zetterstrom, Grant) or Birds of Europe (Jonsson) are the best and most comprehensive. For something a little more pocketable try A Pocket Guide to the Birds of Britain and North-West Europe (Madge, Nurney). A comprehensive Irish guide is The Complete Guide to Ireland's Birds (Dempsey, O'Clery), which is a large format hardback - not good for ID but gives an idea of what is present in Ireland and has distribution maps. It was edited down to form the small paperback A Pocket Guide to the Common Birds of Ireland. For where to see birds, try Where to Watch Birds in Ireland (Hutchinson).