I've always enjoyed H.P. Lovecraft's use of adjectives. He was never at a loss for the perfect word to evoke some subtle gradation of horror. Here are some of my favorites, all contained within a single short story (The Lurking Fear):
abysmal, hideous, unnameable, Charonian, unspeakable, transcosmic, demonaic, charnel, cataclysmic, grotesque, hellish, unhallowed, insane, antediluvian, unclean, sepulchral, diabolic, baneful, cyclopean, accursed, loathsome, festering, noxious, unwholesome, malignant, weird, sinister, leprous, night-spawned, slavering, Cthonic, fulgurous, ensanguined, formless, ghoulish, verminous, nauseous, voiceless, hateful, queer.