I saw your post about ceremony music.
When I was in HS I sang in the chorus and remember singing an Irish Blessing song. Lots of people use the words in speeches and quotes.. but it was beautiful when we sang it. I'm not suggesting someone sing it, but maybe if your ceremony musicians could play it. I found a version of it on youtube http://www.youtube.com/watch?v=Ti3EWCbtZGk&feature=related
If you're looking for something for something a bit more peppy for maybe a recessional maybe "I'm Shipping Up To Boston" - Dropkick Murphys - which has a very Irishy flare.