One of the nicest shower cakes I've seen just had the initials of the bride and groom cut out of fondant with stencils and then a velvet bow at the top, but it was a square cake, not rectangular. The bow was blue, the bride's "color", as were the fondant letters.

If you have time you could get one of those plastic candy molds at the nearest store that sells Wilton type accessories. The melts come in a bunch of colors and the molds include doves, hearts, bells, the traditional wedding stuff, and you could make candy decorations for the cake.

You could just pipe two intertwined hearts on the cake and put the intials of the bride and groom into the hearts, with a congratulatory message piped on.

Or you could get inedible decorations to add to the cake, like a small bride and groom and an arbor for them to walk through, or something similar.

I also saw one cake that was shaped like a bustier, with two cupcakes for the "bosoms", but that would be a lot more involved....

Annie

For tons of inspiration, ideas, tips & techniques, check out cakecentral.com. Everything that you would ever need to know about cake decorating.
Jane

I have given more than a few bridal showers and bridal luncheons, and always decorated the cake like a wedding cake....albeit a small one!...And I had "The cake lady" make them. Decorating cakes is not my forte!
The cakes were 2 tiered and simply piped with lattice on the sides and topped with a shot glass inserted into the cake with fresh flowers in the glass.
For bridal luncheons, we did the traditional charms in the cake, with the ribbons extending thing....looked pretty and was fun.

Here is a link that might be useful: wedding cake charms

i think edible flowers make great cake decoration!

Here is a link that might be useful: edible flowers