We use Chaosium-written modules.
We write homebrew modules.
We've battled cultists.
We've battled monsters.
We've battled Great Old Ones and/or Outer Gods directly.
Most party members survive with their wits intact.
We use creatures from Lovecraft or published sources.
We make up new beasties as needed.
We play Cthulhu d20, not the original BRP version.