Things to see. One of my favorite things in Ireland was the Bus Eireann day trip to Boyne Valley/Newgrange. It's a very affordable and well paced day trip. The driver isn't a guide, they tell you the basics about the stops but stay on the bus. Each stop had enough time to look around without being in a hurry. The stops were Newgrange (stone age passage tombs), Hill of Tara (historic seat of Irish Kings) Trim castle, plus a quick stop at the sight of the Battle of the Boyne.
They offer a second day trip that takes you to Glendalough Abbey ruins and more of a scenic drive through that area.
We picked up our tickets the evening before at the downtown bus station, then showed up the next morning for the trip. I doubt they'll be sold out so booking far in advance isn't necessary.
http://www.buseireann.ie/news.php?id=968&month=Jun