Here are some sample fillings that are possible... actually, the possibility is endless... depends on your personal preference.
Simple fresh cream filling
Mango/Peach filling
Blackforest filling (Fresh Cream + Jam)
Buttercream filling (Chocolate/Original Butter/Vanilla/Coffee etc...
Mousse filling (Chocolate/Strawberry etc)
Blackforest filling with dark cherries
Fresh cream
Fresh cream with fresh fruit e.g. strawberry, banana, peaches.
Concentrated fruit filling (Strawberry, grape, raspberry, blueberry etc.)