WordNet (r) 3.0 (2006):

work of art
    n 1: art that is a product of one of the fine arts (especially a
         painting or sculpture of artistic merit)

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "work of art":
   art object, brainchild, bric-a-brac, classic, composition,
   creation, design, grotesque, kitsch, master, masterpiece,
   masterwork, mobile, museum piece, nude, old master, pasticcio,
   pastiche, piece, piece of virtu, stabile, statue, still life,
   study, virtu, work