My wedding invitations were designed to fold into a neat little square. When I started I had a very rough idea of what I wanted (when I say that I guess I really mean what my fiance wanted, luckily we have similar taste), but mostly played it by ear, a luxury sometimes missed on regular client work for obvious reasons. I also created a RSVP website to allow our friends and family to quickly and easily let us know whether or not they would be attending.
I forget now which print shop I ended up using but I did shop around before finding a supplier with a stock that I wanted while not being too overpriced. They printed very nicely and I posted them out to New Zealand the next day.