Les Crosets in the Portes du Soleil, which is just into switzerland from france has an awesome park at the moment. Les Deux Alpes is always good. Aparently the moon park in Meribel is pretty nice too. Avoriaz is nice, but too small. Good for beginners though.
Of course, the mountain where i ski most doesn't have a damn park, despite them promising one for years! GRRRRRR!