WordNet (r) 3.0 (2006):

supportive
    adj 1: furnishing support or assistance; "a supportive family
           network"; "his family was supportive of his attempts to
           be a writer" [ant: unsupportive]

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "supportive":
   assuring, auspicious, bearing, bolstering, bracing,
   bright with promise, burdened, buttressing, carrying, cheering,
   comforting, condolatory, condolent, condoling, confirmative,
   confirmatory, confirming, consolatory, consoling, corroborating,
   corroborative, corroboratory, encouraging, favorable,
   full of promise, heartening, helpful, holding, hospitable,
   inspiring, inspiriting, looking up, maintaining, of good comfort,
   of promise, pregnant of good, promising, propitious, propping,
   reassuring, relieving, shoring, substantiating, supporting,
   suspensory, sustaining, sustentative, sympathetic, understanding,
   upholding, verificative, verifying