Choosing the music:

Most musicians will make every effort to accommodate particular requests from a couple, but you should have due regard to the appropriateness of a piece for a church service; also, to the style and capabilities of the musicians you have engaged.

"Secular" pop-songs are often best left until the reception, although some can be appropriate for inclusion at the Signing of the Register, when the service is over.

Check the music with the celebrant, as some parishes are stricter than others.

Check out:

http://www.together.ie/Music-Wedd.html