Debussy's Clair de Lune (or "Moonlight") is a beautifully expressive piece of music, with a dreamy quality making it ideally suited for wedding and funeral services, whether held in a church or elsewhere. Because of its mix of long sustained and shorter notes, it is best played on a piano but experience organists can play it with care. Download the piano sheet music, midi and mp3 files.
Pachelbel's Canon (or Canon in D) is a very popular choice for weddings. Originally written for strings, this is an arrangement for piano (or organ) which can be download along with midi and mp3 versions.