The Collaborative International Dictionary of English v.0.48:

Melodious \Me*lo"di*ous\, a. [Cf. F. m['e]lodieux. See
   Melody.]
   Containing, or producing, melody; musical; agreeable to the
   ear by a sweet succession of sounds; as, a melodious voice.
   "A melodious voice." "A melodious undertone." --Longfellow.
   -- Me*lo"di*ous*ly, adv. -- Me*lo"di*ous*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

melodious
    adj 1: having a musical sound; especially a pleasing tune [syn:
           tuneful, melodious] [ant: tuneless, unmelodious,
           untuneful]
    2: containing or constituting or characterized by pleasing
       melody; "the melodious song of a meadowlark" [syn:
       melodious, melodic, musical] [ant: unmelodic,
       unmelodious, unmusical]

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "melodious":
   achingly sweet, agreeable, agreeable-sounding, appealing, ariose,
   arioso, canorous, cantabile, catchy, dulcet, euphonic, euphonious,
   euphonous, fine-toned, golden, golden-tongued, golden-voiced,
   harmonious, honeyed, lyric, lyrical, melic, mellifluent,
   mellifluous, mellisonant, mellow, melodic, music-flowing,
   music-like, musical, pleasant, pleasant-sounding, rich,
   silver-toned, silver-tongued, silver-voiced, silvery, singable,
   songful, songlike, sonorous, sweet, sweet-flowing, sweet-sounding,
   tunable, tuned, tuneful