The Collaborative International Dictionary of English v.0.48:

Unvalued \Un*val"ued\, a.
   1. Not valued; not appraised; hence, not considered;
      disregarded; valueless; as, an unvalued estate. "Unvalued
      persons." --Shak.
      [1913 Webster]

   2. Having inestimable value; invaluable. [Obs.]
      [1913 Webster]

            The golden apples of unvalued price.  --Spenser.
      [1913 Webster]

WordNet (r) 3.0 (2006):

unvalued
    adj 1: having value that is not acknowledged [syn:
           unappreciated, unsung, unvalued]

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "unvalued":
   despised, disliked, lowly, misprized, misunderstood, out of favor,
   thankless, unappreciated, uncared-for, underestimated, underrated,
   undervalued, unlamented, unmissed, unmourned, unpopular,
   unregretted, unsung