there are lots of ideas on this site in the galleries, and of course we have some sites we can post for you to look at..... how simple do you want to make it, do you have a specific thing you wanted on it, and is the sex of the baby known????
How about the cake that is a round cake cut to look like a baby carraige, and the two smaller round cakes as the wheels? There are so many variations of that design around. I'm making one like that for a baby shower at the end of May.