Here are seven pieces that, while not as well-known as more traditional pieces, would still work nicely in a wedding. These particular works were all chosen for their appropriateness in setting the pace for a beautiful and solemn processional or joyful recessional. Most are dominated by long melodies.
"Zion hört die Wächter singen," Wachet auf, ruft un die Stimme, Cantata BWV 140: The fourth movement of this cantata by Bach has a very romantic hue when arranged for strings or even classical guitar and, when played at the right tempo, sets a steady pace for the processional.
"Adagio," Sonata No. 13 in E flat Major, Op. 27: The 3rd movement of Beethoven's 13th piano sonata is contemplative and majestic. If used as a processional, however, the piece will need to be ended before the cadenza that leads into the fast-paced 4th movement.
"Adagio," Serenade No. 10 in B-flat, K. 361 (K. 370a): This third movement of Mozart's serenade for winds has a soaring, plaintive melody.
"Adagio Cantabile," Sonata No. 8 in C minor, Op. 13: The second movement of Beethoven's "Pathétique" sonata, while more well-known than the other pieces on this list, is nevertheless a beautiful work.
"Menuet II," Music for Royal Fireworks: The second half of the final movement of one of Handel's offerings to the King of England is a stately minuet, a courtly dance that emphasized refinement, dignity, and regality.
Tehillim IV (Psalm 150:4-6): If you desire something a little more postmodern and exotic, try the fourth movement of Steve Reich's settings of various Hebrew texts. The repetitive melodic fragments and unmetered rhythm give this upbeat piece a world music flavor.
"Was Gott tut, das ist wohlgetan," Die Elenden sollen essen, Cantata BWV 75: Another excerpt from a Bach cantata, this piece is composed of multiple melodies intertwining in dance-like joy. The activity of the polyphonic voices combined with an upbeat tempo makes this work a fitting recessional.
Also keep in mind the impact the particular arrangement will have on the mood of a piece. A solo instrument will create an atmosphere of intimacy and privacy. A large orchestral arrangement will make everything seem bigger and more grandiose. Yet whether you want a small affair or a large-scale festival, any of these pieces can be adapted to fashion the atmosphere of your choice.