WordNet (r) 3.0 (2006):

blah
    n 1: pompous or pretentious talk or writing [syn: bombast,
         fustian, rant, claptrap, blah]

Moby Thesaurus II by Grady Ward, 1.0:

186 Moby Thesaurus words for "blah":
   Laodicean, Olympian, acedia, aloof, aloofness, apathetic, apathy,
   arid, ataraxia, ataraxy, balderdash, baloney, banausic, barren,
   benumbed, benumbedness, bilge, blah-blah, blahs, blank, blase,
   blather, blatherskite, bloodless, bop, bosh, broken-record, bull,
   bullshit, bunk, bunkum, characterless, cold, colorless, comatose,
   comatoseness, crap, dead, desensitized, detached, detachment, dim,
   disinterest, disinterested, dismal, dispassion, draggy, drearisome,
   dreary, dry, dryasdust, dull, dullness, dusty, effete, elephantine,
   empty, etiolated, everlasting, eyewash, fade, flapdoodle, flat,
   gas, guff, gup, harping, heartless, heartlessness, heavy, hebetude,
   hebetudinous, ho-hum, hogwash, hokum, hollow, hooey, hopeless,
   hopelessness, hot air, humbug, humdrum, in a stupor, inane,
   inappetence, indifference, indifferent, inexcitable, insipid,
   insouciance, insouciant, invariable, jejune, jog-trot,
   lack of appetite, languid, languidness, leaden, lethargic,
   lethargicalness, lethargy, lifeless, listless, listlessness,
   long-winded, low-spirited, malarkey, monotone, monotonous,
   moonshine, nonchalance, nonchalant, numb, numbed, numbness, pale,
   pallid, passive, passiveness, passivity, pedestrian, phlegm,
   phlegmatic, phlegmaticalness, phlegmaticness, piffle, plodding,
   pluckless, plucklessness, pointless, poky, ponderous, poppycock,
   prolix, resignation, resigned, resignedness, rot, scat, shit,
   singsong, slack, sloth, slow, sluggish, sluggishness, solemn,
   sopor, soporific, soporifousness, spiritless, spiritlessness,
   spunkless, spunklessness, sterile, stiff, stodgy, stoic, stuffy,
   stupefaction, stupefied, stupor, superficial, supine, supineness,
   tasteless, tedious, tommyrot, torpid, torpidity, torpidness,
   torpor, treadmill, tripe, uncaring, unconcern, unconcerned,
   uneventful, uninterested, unlively, unvarying, vapid, wind,
   withdrawn, withdrawnness, wooden