I make a chocolate hazelnut mousse with marscapone and heavy cream. Sometimes I add some coffee to it and it is so yummy! It is my most requested filling.
My second would be my white chocolate raspberry filling. You can put that with a white chocolate cake or Lemon cake, or change it up with strawberries.
Toba Garretts (Sp) Chocolate Buttercream with ganache is to die for. I mean really, it's to die for. I don't always use the Godiva Liquor, but use coffee creamer instead, depending on the age of the client. I have also used Baileys in place of the Godiva.
I did a marble cake with oreo cookies and cream filling this week which was pretty good, I of course doctored the recipe as I always do.