Looking for unique wedding party songs. Ideas?

I go to a non-denominational church. For our wedding, my fiance would like to do something unique and instead of a piano or organ, we'd like an acoustic guitar to play. Now we have to figure out songs so I'm open to suggestions. I know we need songs for the seating of grandparents and our parents...and of course the bridal party and then the song I walk down the aisle to. Any ideas as to what would song cool with a guitar?