Mango and any soft-flavored thing, like coconut, pineapple, pecans, hazelnuts.
Raspberries are strong enough to compete and compliment the mango, and taste good with chocolate, too. I think other berries will work, too--especially the red ones.
I'd go for it and see how it tastes--that's what really counts! Make a cake and cut it into portions and combine it with the mousse and different berries, fruits, nuts, etc. and see which one you like the best.
It's not the destination, but the journey!