I'd recommend Chandelure for a good Ghost-type. It's part Fire, has good abilities and its base Special Attack of 145 hits extremely hard. It also learns lots of good Ghost and Fire attacks to take advantage of it. It can also learn Energy Ball (a Grass-type attack) to counter most of its weaknesses.
As Gimmiepie said, Krookodile makes a good choice for a Dark-type cos it has good stats, is obtained fairly early in the game, and has a good physical movepool to take advantage of its high Attack stat.
Sigilyph makes a good choice for a Psychic, due to good stats (especially Speed and Special Attack, with some not-too-shabby defensive stats backing it up). It also has a good ability in Magic Guard, which protects it from indirect damage. On top of that, it has a good special-based movepool.
Scrafty is another Dark to consider due to being part Fighting and it learns good physical attacks that abuse its good Attack stats. It even has good abilities too, I'd recommend getting one with Moxie since it boosts the Attack stat with each KO it does on the opponent.
Golurk is also nice if you want a physical Ghost, due to a good movepool including Shadow Punch, Earthquake and Hammer Arm. Shadow Punch and Hammer Arm hit pretty hard if you get the ones with the Iron Fist ability. Never get ones with Klutz though, they stink.