Mozart wrote the Exsultate, Jubilate solo motet in 1773 while visiting Milan. It's a glorious work for solo soprano, and I have had the privilege of accompanying a very good soprano when she performed it. It is not an easy piece for either singer or accompanist, but definitely gives a feeling of "whew, what a ride!" when you're done. The Alleluia is the final section, and bubbles over with joy and exuberance - a perfect classical underscore for a wedding recessional.
Personally, I would suggest that you choose an instrumental version of the Alleluia if you are going to use it for your recessional. First, you have to know a cracking good soprano willing to sing this. Second, because of its vocal virtuosity, having a singer do it would (in my opinion) take away the focus from the wedding couple.
I've included a great mp3 version of the Alleluia movement below performed by the Canadian Brass, which is a wonderful choice for exit music - who doesn't want to walk out to fanfare? But for fairness' sake, I've also included a vocal version so you can hear what I'm talking about in its original vocal form.