I make cupcake bath bombs for gifts, and I LOVE the cream cheese frosting FO from Brambleberry. It smells absolutely the same as cream cheese frosting, which I could eat a tub alone. Vanilla is also one of the obvious choices, Brambleberry also has a "Warm Vanilla Sugar." I don't know if you even shop Brambleberry, but you could surely find these types of fragrances through other vendors.
I've used orange and strawberry FO on seperate occasions for the cake portion and named them berries & cream cupcakes and orange cream cupcakes

I've also done spearmint green frosting with chocolate espresso FO for the cake part and named it mint chocolate chip.
You could do a caramel icing, a coconut icing, butter cream icing, pineapple cake part ... pumpkin cake part or ginger snap or snickerdoodle cake part for the upcoming holidays if you were looking for something festive...
Hope this helps get the ball rolling!