This music is traditionally played as the bridal party processes. Since here's really no way to tell how long each couple will take to walk the aisle, a very flexible song is preferable.
Canon in D
A bride might choose to process to the more traditional pieces of “Bridal Chorus” or “Trumpet Voluntary,” or choose a less traditional or more personal piece for her entrance. Here are only a few suggestions.
Con Te Partiro
Unless otherwise requested by the priest, the Mass of Renewal is what is usually played during weddings. (With the exception of the the Celtic Alleluia.)
Mass of Renewal
(Starting at 4m32s)
Depending on the number of family, friends, and other invited guests, you may choose one or two songs for this part of the ceremony. You may also choos from the "Offertory Hymns" category.
One Bread, One Body
Flowers to Mary
This takes place right after communion. As the now Wife and Husband dedicate their union to the Mother of God, the Ave Maria is usually played. The couple may also elect to sign the wedding licence at this point. (The Ave Maria is a longer song, so please, take your time!)
Ave Maria (Schubert)