There is also the rather rare A Preliminary Survey of the Ancient Monuments of Northern Ireland, published in 1940. A good copy will set you back a bit now. It's probably in the bigger libraries. There's a battered copy on abebooks at the moment for £21.

It is in no way comprehensive, but includes most of the megalithic tombs in the north.

There are some interesting monologues in the Discovery series, too: http://www.discoveryprogramme.ie/publication_mono.html