We have picked Metallica - Nothing Else Matters
If you want to hear it...
http://www.youtube.com/watch?v=erPnyi90cIc
... its a slow start, so skip to 1:40 to start listening to it.
Oh and we haven't decided if this will be the processional or the first dance. My half sister is playing violin for the ceremony, so I need to talk to her. My brother plays guitar and can play this song, so I am sure she can play it. (She's a professional)