I made this Stegosaurus cake for my sons 5th birthday, inspired by a photo I saw on pinterest. Link
I started out with a 20cm chocolate cake iced green buttercream, luckily it baked with a lopsided top as this worked well for the stegosaurus body.
Used a template from google images and traced around the template onto coloured card for head, tail and spikes. Then just pushed cardboard spikes into icing.
A very quick and easy cake, think of all the other possibilities of cake and cardboard you could do :-)