WordNet (r) 3.0 (2006):

sourpuss
    n 1: someone with a habitually sullen or gloomy expression [syn:
         sourpuss, picklepuss, gloomy Gus, pouter]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "sourpuss":
   bellyacher, brooder, complainer, crab, crank, crosspatch,
   depressive, gloomy Gus, griper, grouch, grouser, kicker, killjoy,
   malcontent, melancholiac, melancholic, mope, sorehead, spoilsport,
   wet blanket