WordNet (r) 3.0 (2006):

voyeurism
    n 1: a perversion in which a person receives sexual
         gratification from seeing the genitalia of others or
         witnessing others' sexual behavior

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "voyeurism":
   active algolagnia, algolagnia, algolagny, amphierotism,
   autoeroticism, bisexuality, coprophilia, curiosity, curious mind,
   curiousness, exhibitionism, fetishism, ghoulishness,
   heterosexuality, homoeroticism, homosexualism, homosexuality,
   incest, incestuousness, inquiring mind, inquisitiveness, interest,
   itch for knowledge, lesbianism, lively interest, masochism,
   meddlesomeness, mental acquisitiveness, morbid curiosity,
   narcissism, necrophilia, nosiness, officiousness, paraphilia,
   passive algolagnia, pedophilia, prurience, prurient interest,
   prying, sadism, sadomasochism, sapphism, scopophilia, scotophilia,
   sexual inversion, sexual normality, sexual preference,
   swinging both ways, thirst for knowledge, transvestitism,
   tribadism, tribady, zooerastia, zoophilia