WordNet (r) 3.0 (2006):

superstar
    n 1: someone who is dazzlingly skilled in any field [syn: ace,
         adept, champion, sensation, maven, mavin,
         virtuoso, genius, hotshot, star, superstar,
         whiz, whizz, wizard, wiz]

Moby Thesaurus II by Grady Ward, 1.0:

94 Moby Thesaurus words for "superstar":
   A per se, ace, big name, boss, celebrity, champion, chief,
   commander, constellation, crackerjack, cynosure, danseur noble,
   dean, diva, electronics king, feature attraction, figure,
   first tragedian, first-rater, folk hero, fugleman, galaxy, genius,
   good hand, great, great man, head, headliner, heavy lead, hero,
   heroine, higher-up, honcho, idol, immortal, important person,
   jeune premier, king, laureate, lead, leader, leading lady,
   leading light, leading man, lion, luminaries, luminary, magician,
   mahatma, man of genius, man of mark, master, master hand,
   master spirit, mastermind, name, nonpareil, notability, notable,
   paragon, paramount, past master, person of note, personage, pleiad,
   pop hero, popular hero, popular idol, practiced hand,
   prima ballerina, prima donna, principal, prodigy, protagonist,
   public figure, ruler, sage, senior, singer, skilled hand,
   social lion, somebody, star, superior, superman, the greatest,
   the most, top dog, topnotcher, virtuoso, whiz, wizard, wonder,
   worthy