Buttercream & cream-cheese icings, mousse fillings, and chocolate glazes can all freeze successfully. The butterfat content helps keep their (fairly dense) textures smooth & creamy throughout the freezing/defrosting stages. The bane in freezing any mixture is the formation of large ice crystals.
"Where love has entered as the seasoning of food, I believe that it will please anyone." ~ Plautus: Casina