There is Golurk,Cofagrigas,Chandulure and all of their pre-evolutions as Ghost Types. For Dark Types there is Hydregion,Bisharp,Krookodile and all of their pre-evolutions.
You could also have a Sableye.
Found in the challengers cave after you finish the game.
If you need it before the E4,I have 4 sableyes ready for trade,I can trade as soon as I get Wi-Fi,(which won`t be long)