WordNet (r) 3.0 (2006):

crystal ball
    n 1: a glass or crystal globe used in crystal gazing by
         fortunetellers

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "crystal ball":
   aftertime, afteryears, astrology, augury, by-and-by, clairvoyance,
   course ahead, crystal gazing, determinism, distant future,
   divination, divining, eventuality, expectation, foresight,
   fortunetelling, forward look, future, future tense, futurism,
   futurity, haruspication, haruspicy, hereafter, horoscopy,
   immediate future, immediate prospect, imminence, mantic, mantology,
   near future, offing, outlook, palm-reading, palmistry,
   posteriority, prediction, probability, project, prophecy, prospect,
   pythonism, sorcery, the future, the morrow, the sweet by-and-by,
   time ahead, time just ahead, time to come, tomorrow