A popular theme that works well for either a boy or a girl is a clown or other circus_related cake. They are usually very bright and colorful, which makes for instant attraction and a great focal point for a party table.
Birthday cakes are one of the most important things of interest in any birthday celebration. A birthday party with no tasty birthday cake will not make that event complete. Regardless of whether or not you are an adult or a kid, you would always be happy to have a cake around. Children are always full of life when they see cakes around and the more unique your cake is, the more your party becomes unique.