Diamond wedding rings are made by jewel crafters.
Clothes, best suggestoin would be to use the fashion link at the left of this page and find something you both would like to wear. Once you've decided your atire, try and find that particular clothing in the bazaar.
Don't forget wedding cake and drinks. You may have to hire a brewer and/or baker if you're looking for something specific.
Sometimes GM's do the ceremony, but I've seen paladins/sk's/cleric/guildleaders/druids hold them as well.