A lovely processional or recessional for the organ is the Trumpet Voluntary by Purcell. Class! Almost any baroque music is lovely for organs and suitable for before and after the ceremony: I love Bach especially. Some of the fugues are particularly nice for recessionals (they're a bit long for before). For during (during Communion, etc.), ask for pieces that are more contemplative as you don't want to break the mood of the ceremony itself. (Any experienced church organist will be able to trot out any number of appropriate pieces. Just give them an idea of the mood you want, and ask them to play the pieces for you to make sure you don't hate them.)
My bar-none fav for the father-bride dance: "Unforgettable", duet of Nat King Cole and Natalie Cole (a posthumous duet between father and daughter). The first dance should be something that has meaning for the bride and groom.
If you're going to have a mixed batch of generations, remember to include some jazz standards, retro, and stuff that the older folks will like, as well as modern pop/rock stuff for the younger. If you want something that will appeal to all generations, look to things like salsa and other world musics (very hip, too) as well as jazz standards and retro.
