You generally have a more religeous crowd so you have some latitude you wouldnt have in other gigs. I think the Irish Prayer is very nice and eveyone will learn all the words quickly.

May the road Rise up to meet you
May the wind be ever at your back
May the sun shine warm upon your face
May the rain fall soft upon your fields
Until we meet again, may god hold you
In the hollow of his hand.

Its a nice sentiment which I think is more important than a dancing tune, if they are going to remember it.

Also the Mingulay Boat song is very nice for ending sets with.

sigurd