I know, you meant songs with meaningful lyrics to sing along.
Well, I don`t know if there are lyrics to this song I heard on the IrishActs website. Its track 2 => Leanbh Mo Chroi (Child of my Heart). Its an amazing instrumental piece. A touching one...

It can be found on :
http://www.irishacts.com/

Another song that comes to mind is "You raise me up"

Hope you have a great time gigging !!