I don't know your team, so I can't get specific Pokemon for you. Here are some pointers to defend against it though:
Dark Types. Both Ghost and Psychic are weak to Dark type moves like Crunch or Dark Pulse. If you're having trouble, teach your Pokemon a few Dark moves.
Ghost Types. Both Ghost and Psychic are weak to Ghost type moves like Shadow Ball or Shadow Sneak. If you're having trouble, teach your Pokemon a few Ghost moves.
Special Walls. All but 5 of the 48 Psychic moves are special moves, and 11 of the 17 are special moves as well. A Pokemon with high Special Defense should shrug these off fairly easily.
And, as always, use type advantages. If it is a Ghost-Poison type like Gengar, throw a Dark move at it. If it is a Psychic-Fighting like Medicham, throw a Flying move at it.
