They also had a link to LookAroundIreland. A site using interactive photo panoramas and googlemaps to show tourist and heritage spots around Ireland. Including Tara and Liafail. Also a fantastic panorama from the central chamber of Newgrange.
I don't know how long this has been around on www.archaeology.ie It is live Record of Monuments and Places map... you can zoom in anywhere in Ireland to see archaeological features on detailed map, highlight them with a box and then it will list what they are, unfortunately it doesn't actually give the name of the specific feature only the type like 'hilltop fort' or ''barrow.
They still don't seem to have a straight list of national monuments available on the web. the one on the OPW site was taken down because they said there were too many errors on it.
Aerial photos of Ireland are available at the National Parks and wildlife service website for Ireland, I don't know how much of Ireland they cover but I seen numerous areas which are better quality and more recent then googlemaps. It primarily shows special conservation areas with aerial photos overlayed with contours.
I've already mentioned Megalithmania and the Modern Antiquarian.
Megalithomania Reports on numerous archaeological sites in Ireland with additional geographic information. You can view notes, photos and then view it place marked in googlemaps and search to view other megaliths in the area.
The Modern Antiquarian uses a similar system Juliana Cope's online personal antiquarian guide. I also discovered their own downloadable kmls for googleearth, with all the sites marked with a photo popping up beside aswell. Even has google v4 and v3 version