The Collaborative International Dictionary of English v.0.48:

Perfectionist \Per*fec"tion*ist\, n.
   1. One pretending to perfection; esp., one pretending to
      moral perfection; one who believes that persons may and do
      attain to moral perfection and sinlessness in this life.
      --South.
      [1913 Webster]

   2. A person who insists on perfect results from himself or
      from others, in any endeavor.
      [PJC]

WordNet (r) 3.0 (2006):

perfectionist
    n 1: a person who is displeased by anything that does not meet
         very high standards

Moby Thesaurus II by Grady Ward, 1.0:

89 Moby Thesaurus words for "perfectionist":
   Babbitt, Leibnizian, Leibnizian optimist, Middle American,
   Philistine, Pollyanna, anal character, aspirant, aspirer,
   bourgeois, bright, burgher, captious critic, censorious, cheerful,
   chiliast, chiliastic, choicy, choosy, compulsive character,
   conformer, conformist, conscientious, conventionalist,
   couleur de rose, critical, demanding, discriminating,
   discriminative, exacting, fastidious, formalist, fuss-budget,
   fusspot, fussy, hopeful, hoper, irrepressible optimist,
   methodologist, meticulous, middle-class type, millenarian,
   millennialist, millennialistic, millennian, model child,
   nit-picking, nitpicker, obsessive, optimist, optimistic,
   organization man, parrot, particular, pedant, perfectibilist,
   perfectibilitarian, perfectionistic, philosophical optimist, picky,
   plastic person, precise, precisian, precisianist, precisianistic,
   precisionist, priggish, prudish, punctilious, purist, puristic,
   puritanic, ray of sunshine, rose-colored, roseate, rosy,
   scrupulous, selective, sensitive, sheep, square, stickler, strict,
   sunny, teenybopper, trimmer, upbeat, utopian, yes-man