One thing I heard when Eduardo asked his wedding photography picture question was that this wedding will be on the beach, at night. Talk about a tricky lighting setup! No ceilings to bounce flash off of. And unless he can get an assistant to lug around a strobist syle setup with flashes, stands, umbrellas to do group or staged shots, I think his best bet (assuming he has a DSLR and a separate flash) is to get a light modifier like a Gary Fong Lightsphere or Sto-Fen Omnibounce if he’s using the flash on camera. Or maybe get a bracket to get the flash off camera and raised up somewhat, in addition to a diffuser.
Good luck Eduardo!