WordNet (r) 3.0 (2006):

sadistic
    adj 1: deriving pleasure or sexual gratification from inflicting
           pain on another [ant: masochistic]

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "sadistic":
   Draconian, Tartarean, animal, anthropophagous, atrocious, barbaric,
   barbarous, beastly, bestial, bloodthirsty, bloody, bloody-minded,
   brutal, brutalized, brute, brutish, cannibalistic, cruel,
   cruel-hearted, demoniac, demoniacal, devilish, diabolic, fell,
   feral, ferocious, fiendish, fiendlike, fierce, hellish, infernal,
   inhuman, inhumane, monstrous, murderous, perverse, ruthless,
   sanguinary, sanguineous, satanic, savage, sharkish, slavering,
   subhuman, truculent, unchristian, uncivilized, unhuman, vicious,
   wolfish