I often play organ at weddings around Rochester, especially at Chapel Hill, and I thought it might be helpful to collect some information about wedding music here.
A typical wedding will usually have music in these places:
Prelude (as guests are coming in, usually starting 15-20 minutes before the official start time; these pieces are usually chosen by the organist, as the bride won't hear them)
Seating of the Mothers (not always done)/Bridesmaids' processional (sometimes 2 separate pieces, sometimes just 1 for both groups): usual choices are "Jesu, Joy of Man's Desiring," or Schubert's "Ave Maria"
Bride's processional: Pachelbel's "Canon" is commonly done here, and Wagner's "Bridal Chorus from Lohengrin" as well; the Clarke "Trumpet Voluntary" is also nice, and the Bach "Arioso" is a good one to walk to
Sometimes, a quiet moment (unity candle or sand, sometimes Communion): maybe "Air," by Bach, or something more folksy, like "Ashokan Farewell," "The Water is Wide," or "Red is the Rose" (Chapel Hill, like most churches, has a piano, which can make a nice change for a quiet time in the ceremony)
Recessional (where the bride and groom walk back down the aisle and out): Mendelssohn's "Wedding March" or Handel's "Rejouissance" ("Rejoicing") are often done here; also, trumpet tunes by Clarke, Charpentier, Purcell, or Mouret are all good (they don't need a real trumpet)
Postlude (usually 2 or 3 festive pieces, and usually chosen by the organist)
In the last 10-20 years, brides have been choosing pop songs for their weddings much more frequently. It's a great idea to have things that are meaningful to the bride and groom, and I have played lots of these songs at weddings. But, I try to remind people to keep two things in mind: the song you love so much might have absolutely no meaning to most of the people at the wedding; and it's probably going to sound a little weird on an organ even to people who know it.
I hope that gets you started! Please email me at david (at) (this domain name) if you have any questions.