WordNet (r) 3.0 (2006):

Don Juan
    n 1: a legendary Spanish nobleman and philanderer who became the
         hero of many poems and plays and operas
    2: any successful womanizer (after the legendary profligate
       Spanish nobleman)

Moby Thesaurus II by Grady Ward, 1.0:

103 Moby Thesaurus words for "Don Juan":
   Artful Dodger, Casanova, Circe, Lorelei, Lothario, Machiavel,
   Machiavelli, Machiavellian, Parthenope, Romeo, Siren, actor,
   amoroso, bamboozler, beau, befuddler, beguiler, boyfriend,
   caballero, cavalier, cavaliere servente, charmer, coquette,
   counterfeiter, debauchee, deceiver, deluder, dissembler,
   dissimulator, dodger, double-dealer, duper, enchanter, enchantress,
   enticer, entrancer, esquire, faker, fellow, femme fatale, flame,
   flirt, fooler, forger, gallant, gay deceiver, gay dog, gigolo,
   hoaxer, hypnotizer, inamorato, inveigler, jilt, jilter, joker,
   jokester, kidder, lady-killer, leg-puller, libertine, love-maker,
   lover-boy, man, mesmerizer, misleader, necker, old man, petter,
   philanderer, plagiarist, plagiarizer, playactor, practical joker,
   profligate, ragger, rake, rakehell, rip, role-player, roue,
   rounder, seducer, seductress, sheik, siren, skirt chaser, spoofer,
   squire, sugar daddy, swain, swinger, tease, teaser, tempter,
   temptress, vamp, vampire, walking phallus, wanton, wolf,
   woman chaser, womanizer, young man