butter icing made with part butter, part cream cheese?
Favourite at the M&T group I make cakes for is cut up grapes, strawberries and bananas in cream.
Did an 'emergency' filling last week of butter/icing sugar/hot chocolate powder (didn't have enough icing sugar to do just that) and that was pretty successful
If you do jam, it spreads better if you heat it first (has a nicer consistancy too)
Chocolate spread is nice too, as is chocolate spread and peanut butter if you don't have a nut problem.