The Collaborative International Dictionary of English v.0.48:

Unsung \Unsung\
   See sung.

WordNet (r) 3.0 (2006):

unsung
    adj 1: not famous or acclaimed; "an obscure family"; "unsung
           heroes of the war" [syn: obscure, unknown, unsung]
    2: having value that is not acknowledged [syn: unappreciated,
       unsung, unvalued]

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "unsung":
   anonymous, despised, disliked, disregarded, ignotus, inconspicuous,
   inglorious, insignificant, little known, lowly, misprized,
   misunderstood, nameless, no credit to, obscure, out of favor,
   renownless, silent, thankless, unappreciated, uncared-for,
   uncelebrated, undeclared, undistinguished, unexpressed, unfamed,
   unglorified, unheard-of, unhonored, unidentified, unknown,
   unlamented, unmentioned, unmissed, unmourned, unnotable, unnoted,
   unnoticed, unpopular, unproclaimed, unpronounced, unpublished,
   unrecognized, unrecorded, unregretted, unremarked, unrenowned,
   unsaid, unspoken, untalked-of, untold, unuttered, unvalued,
   unvoiced, unwritten, wordless