The cool thing about the groom cake is that you can have some fun with it. In my 22 years of being a wedding DJ i've seen some very creative stuff. If you looked at the history of this blog you will see that I often post groom cake photos. Here is one that I found to be very cool. A cake in the shape of an acoustic guitar.
Although it's hard to tell in the photo the guitar actually had strings on it.

Steve Bergeron
www.bandstandmusic.com
www.bandstandmusic.blogspot.com