I made my own birthday cake last weekend and decided on one I saw posted on Slashfood called 'The Elvis Cake'.
Banana cake with chocolate chips, peanut butter frosting and topped with chocolate shavings.
I used cake flour, butter, and regular chocolate chips in the cake and then scharfenburger 62% cocoa shavings on the entire outside. I also added an extra 1/2 cup of peanut butter and 1/4 cup butter to the frosting to make it more peanut buttery (I'm a frosting girl). Oh, and I used buttermilk instead of milk in the frosting. This added a nice, balancing tartness to the entire cake.
Every one of us went crazy over it. It stayed moist for four days without refrigeration and was impossible to eat without milk. Also impossible to have anything but a small piece because it was so rich (and yet oddly light). The cake was lightly banana-flavored, not overpowering at all. I did not add the recommended cayenne and cannot imagine it in this cake - for me it would not work well.
Highly, highly recommended. My best friend now demands i make it for her birthday in a month and that I rename it after her instead of The King.