The thought of moving to Barcelona still pumps in my head and I cannot stop thinking on how it will be to organize my wedding there, right on the beach. With a small audience will be a perfect wedding. ;-) well, perfect for us. We should thou get civil married here in our country of residence because you have to be civil married in order to have a wedding, being on the beach or not.
Here is what I've found just looking for 3 minutes, with the help of our dear friend Google:
Destination Weddings in Barcelona: http://weddings.about.com/od/weddinglocations/a/BarcelonaWeddin.htm
And also this one: http://www.barcelonawedding.com/types-of-ceremony/
And I found this beautiful blog with lots of information and things you need for a wedding in Barcelona, but not only, it's a bout weddings in the whole Spain: