There isn't one place that lists sites for options for Catholic wedding music. Each diocese and parish (and sometimes each organist) has it's own regulations, so it's important to find out what those are. I found it very helpful to narrow down selections at home before meeting with the organist (in fact we had everything in order prior to meeting with him) and it looks like on various forums, including WeddingBee, many brides are looking for music resources.
Here are the general guidelines from the Diocese of Buffalo.
Wedding-specific song sites (please add more to the list if you know of any!):
St. Patrick Cathedral in New York
St. Clement Catholic Church
St. Paul Cathedral in Pittsburgh
Diocese of San Diego [pdf file of guidelines and suggestions]
Regis University [pdf file of guidelines and suggestions]
Catholic Books that address wedding/nuptial mass music:
Celebrating Marriage: Preparing the Roman Catholic Wedding Liturgy [I have personally not used this resource]
Catholic Song Sites in general:
Spirit and Song
Tomorrow I will post more about the music we included in our nuptial mass.