WordNet (r) 3.0 (2006):

windbag
    n 1: a boring person who talks a great deal about uninteresting
         topics [syn: gasbag, windbag]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "windbag":
   Captain Bobadil, Gascon, Texan, agreeable rattle, babbler,
   big mouth, big talker, blab, blabberer, blatherer, blower,
   blowhard, blusterer, boaster, brag, braggadocio, braggart,
   chatterbox, chatterer, fanfaron, gabber, gabbler, gasbag,
   gasconader, gibble-gabbler, great talker, hector, hot-air artist,
   idle chatterer, jabberer, jay, magpie, miles gloriosus,
   moulin a paroles, patterer, prater, prattler, rattle, windjammer,
   windy, word-slinger