Diaper cakes are my favorite centerpieces for showers. Not only can you customize them to any theme you've chosen, you have the option of making one yourself or ordering one. There are many online vendors who sell them. They are great conversation starters, the guests always comment on them and they are practical for the mom-to-be. Here are some pictures to show how you can customize them:
The first three are from Lil Dumplin Diaper Cakes and the last two are from babycakesinc.com. They make the most adorable centerpieces!