I need a wall for competitive battling, and I want something that can actually attack.
Okay first off, you're not looking for a wall. Walls are something like Chansey or Gliscor, who have great defenses and can't to squat for damage. As for bulky attackers, any of these will work fine (I'm assuming you're playing OU):
There are also these Pokémon that I couldn't find sprites for: