Cake flavour ideas please

I am making a Frozen cake for a 7 year old (family party with the only childbeing the birthday girl). I'm going to use blue Buttercream frosting to cover it, so it will be vanilla flavoured. Can anyone suggest ideas for the flavour of the cake underneath? I'd usually go with chocolate, which would probably be ok with blue frosting but not sure on the flavour combination? TIA.

A very nice Buttercake would go well.

Couple of very good recipes for you to try, which one depends how you choose on ingredients.

A Basic Buttercake

185 gms butter softened
1 cup caster sugar
1 tsp vanilla essence
3 egg large
2 cups self-raising flour
1/4 cups milk
Preheat oven to 180C and grease a 20 cm cake tin well.
In a large bowl, beat the butter, sugar and vanilla together with an electric mixer
until light and creamy.
Add the eggs one at a time and beat well after each addition.
Sift the flour over the mixture alternately with the milk, adding a third at a time.
Stir in lightly.
Spoon batter into prepared tin and bake for 50-60 minutes or
until a skewer pulls clean from the middle of the cake.
Cool cake in tin for a few minutes before turning out onto a wire rack.
Cake can be iced or dusted with icing sugar if desired.

Best Butter Cake With French Butter Cream Frosting

1 cup butter
4 eggs
1 teaspoon salt
1/2 teaspoon soda
2 teaspoons vanilla
2 cups sugar
3 cups flour
1 teaspoon baking powder
1 cup buttermilk
Cream butter, gradually add sugar.
Blend in eggs, one at a time, then sift and combine flour, salt, baking powder and soda.
Combine buttermilk with vanilla.
Add milk and flour mixtures alternately to creamed mixture, ending with dry mixture.
Mix well.
Cake batter into greased cake tin.
Bake at 325° for 40 - 55 minutes
(Tooth Pick Test - to See If It Comes Out Clean) for Doneness.

French Butter Cream Frosting:
2/3 cup sugar
1/4 cup flour
1/4 teaspoon salt
3/4 cup milk
1 cup cold butter
1 teaspoon of vanilla extract
Place sugar, flour and salt in saucepan and mix thoroughly, stir in milk.
Cook over medium heat and stir constantly until very thick.
Remove from heat and pour into a medium mixing bowl.
Cool to room temperature.
Add 1/2 cup butter at a time (cut into several pieces) and beat at medium-high speed until smooth. Add vanilla and beat well.
Chill icing for a few minutes before decorating.
Iced cake must be refrigerated until serving time.
Makes 2 cups

I saw blue velvet cake recently for a baby shower - will see if I can find a recipe

http://www.food.com/recipe/blue-velvet-cake-329332