Nutella is one of my favorite sweet treats! You can use Nutella as a topping for many different things. It also works great in many baked goods. I will list my favorite ways of using it in baking as well.
As for Nutella as a topping, often times I will put it on the following:
graham crackers (or use the Nutella, crackers, and marshmallows for smores!)
When baking, consider using it in your favorite cake batter (melt it down first), an ingredient in the frosting, or as a filling for cupcakes. It's great swirled into blondie brownie batter as well or spread on top of milk chocolate brownies. Use it as a frosting for cookies or as the "glue" to hold decorations on cakes or cupcakes. It's great mixed into the marshmallow and butter mixture for rice krispy treats as well.