Make sure that the processional is in even time like 2/4 or 4/4. A 3/4 beat is great for a waltz, but not to march in with.
I am not a big fan of the Lohengrin Wedding march or the Mendelssohn Midsummernights Dream one either. I am not superstitious, but have you read the story behind these tunes?
Purcell Trumpet Voluntary or Trumpet Tune are also very good, but a bit overplayed!
Telemann has a series of 12 Heroic Marches that are excellent. With titles like "Honor", "Grace", "Joy", they provide the proper sound and musical context for wishing somebody all the best for a life together!
Music can be found:
http://www.sibeliusmusic.com/cgi-bin...?scoreid=51469
and here:
Werner Icking Music Archive: Georg Philipp Telemann
In German, this is called Heldenmusik. You will have to combine the 3 string parts for the organ