Who are the three Pokemon with secret words in Pokepark?

The three Pokémon with secret words in Pokémon Park Wii are:

* Pikachu: "Pika!"

* Eevee: "Eevee!"

* Piplup: "Piplup!"

While these words aren't exactly "secret," they are the specific cries that need to be used to initiate special events or unlock certain areas in the game.