The song to which Edward and Jasper each walk down the aisle: "Songbird" by Eva Cassidy
The song Kathleen sings, accompanied by Ashton: "Halo" by Beyonce (sorry, embedding disabled).
Kathleen's version is more soulful, less poppy.
Herbie Hancock's "Cantaloupe Island", which plays during the cocktail hour at the reception:
Jasper and Edward's first song, though the version in the story is the studio version - which I simply could not find on YouTube:
Their second song, "Angels" by Robin Thicke (from Robin's site, so no embedding).
And the final song, of course, has already been linked here - it was the first song posted on my blog. :)