The Collaborative International Dictionary of English v.0.48:

Unpretentious \Unpretentious\
   See pretentious.

WordNet (r) 3.0 (2006):

unpretentious
    adj 1: lacking pretension or affectation; "an unpretentious
           country church"; "her quiet unpretentious demeanor" [ant:
           pretentious]
    2: not ostentatious; "his unostentatious office";
       "unostentatious elegance" [syn: unostentatious,
       unpretentious, unpretending] [ant: ostentatious,
       pretentious]
    3: exhibiting restrained good taste; "the room is pleasant and
       understated" [syn: understated, unostentatious,
       unpretentious]

Moby Thesaurus II by Grady Ward, 1.0:

83 Moby Thesaurus words for "unpretentious":
   altruistic, arcadian, bucolic, candid, committed, consecrated,
   dedicated, devoted, direct, discreet, disinterested, genuine,
   homely, homespun, honest, humble, humble-looking, humble-visaged,
   humblest, inartificial, inglorious, innocuous, least, low, lowest,
   lowliest, lowly, mean, meek, modest, native, natural, naturelike,
   pastoral, plain, poor, rural, sacrificing, self-abasing,
   self-abnegating, self-abnegatory, self-denying, self-devoted,
   self-effacing, self-forgetful, self-immolating, self-neglectful,
   self-neglecting, self-renouncing, self-sacrificing,
   self-unconscious, selfless, simple, small, straightforward,
   teachable, unacquisitive, unadorned, unaffected, unambitious,
   unartificial, unaspiring, unassuming, unboastful, undesigning,
   undisguising, undissembling, undissimulating, undistinguished,
   unembellished, unfeigning, unimportant, unimposing, unobtrusive,
   unostentatious, unpossessive, unpresuming, unpresumptuous,
   unpretending, unselfish, unsparing of self, unspoiled,
   unvarnished