None as we are an atheist household & my DCs have not been christened. The point of a godparent is to ensure the child is brought up in the Christian faith, which wouldn't be at all applicable for us.
If we had a non religious naming ceremony there still wouldn't have been any 'significant adults' that were to play a special role in the child's life. Either you take an active part & interest in the child's life or you don't.
except in my ex sils family where such a role is used to demonstrate how speshul that person is to the mother & expected to be reciprocated