Ashley, forgive me if you've already said, but are you having the wedding here or in the US? Are you having a big do or a little one?
The reason is, yes most wedding cakes here are fruit cakes, iced with marzipan and are really very nice. Different, but nice. I know that people here have found bakers to do a more American style cake, but most places just do the fruit cake. It is somewhat in the fashion of the US Christmas fruit cakes, but honestly, it is better. I love them and hate US fruitcake, so there ya go!
We had fruitcake because we had a small wedding in Scotland with just my sister and his immediate family attending.
The tradition seems to be that for people who can't make it to wedding, you mail a small square of the cake to them. There are even special little boxes that are made for this purpose.
The other part of the tradition is that you save the top of the cake for the first born child. I'm not sure if the parents or the child are supposed to eat it, but it is definately for the birth of the firstborn. I've heard some people say it was for the firstborn's first birthday as well so I expect across the UK the tradition may be slightly different depending on the area you're in.
Anyway, that's what I know, which ain't much, but oh well!