The Collaborative International Dictionary of English v.0.48:

Wellwisher \Well"wish`er\, n.
   One who wishes another well; one who is benevolently or
   friendlily inclined.
   [1913 Webster]

WordNet (r) 3.0 (2006):

well-wisher
    n 1: someone who shares your feelings or opinions and hopes that
         you will be successful [syn: sympathizer, sympathiser,
         well-wisher]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "well-wisher":
   Maecenas, abettor, acquaintance, admirer, advocate, aficionado,
   alter ego, angel, apologist, backer, best friend, bosom friend,
   brother, buff, casual acquaintance, champion, close acquaintance,
   close friend, confidant, confidante, defender, dependence,
   encourager, endorser, exponent, familiar, fan, favorer, fellow,
   fellow creature, fellowman, friend, friend at court,
   inseparable friend, intimate, lover, mainstay, maintainer,
   neighbor, other self, paranymph, partisan, patron, pickup,
   promoter, protagonist, reliance, repository, second, seconder,
   sectary, sider, sponsor, stalwart, standby, support, supporter,
   sustainer, sympathizer, upholder, votary