The Collaborative International Dictionary of English v.0.48:

Flashy \Flash"y\, a.
   1. Dazzling for a moment; making a momentary show of
      brilliancy; transitorily bright.
      [1913 Webster]

            A little flashy and transient pleasure. --Barrow.
      [1913 Webster]

   2. Fiery; vehement; impetuous.
      [1913 Webster]

            A temper always flashy.               --Burke.
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   3. Showy; gay; gaudy; as, a flashy dress.
      [1913 Webster]

   4. Without taste or spirit.
      [1913 Webster]

            Lean and flashy songs.                --Milton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

flashy
    adj 1: tastelessly showy; "a flash car"; "a flashy ring";
           "garish colors"; "a gaudy costume"; "loud sport shirts";
           "a meretricious yet stylish book"; "tawdry ornaments"
           [syn: brassy, cheap, flash, flashy, garish,
           gaudy, gimcrack, loud, meretricious, tacky,
           tatty, tawdry, trashy]
    2: (used especially of clothes) marked by conspicuous display
       [syn: flashy, gaudy, jazzy, showy, sporty]

Moby Thesaurus II by Grady Ward, 1.0:

108 Moby Thesaurus words for "flashy":
   Gongoresque, Johnsonian, ablaze, affected, aflame, bedizened,
   big-sounding, blatant, blazing, blinding, brave, bravura, braw,
   brazen, burning, cheap, chichi, chintzy, convoluted, cosmetic,
   crude, daring, dashing, declamatory, dressy, elevated, euphuistic,
   exhibitionistic, facile, flamboyant, flaming, flaring, flash,
   flashing, flaunting, florid, frilly, frothy, fulgurant,
   fulgurating, fulsome, gallant, garish, gaudy, gay, glaring, glib,
   glittering, grandiloquent, grandiose, grandisonant, high-flowing,
   high-flown, high-flying, high-sounding, highfalutin, inkhorn,
   insubstantial, jaunty, jazzy, labyrinthine, lexiphanic, lofty,
   loud, lurid, magniloquent, meretricious, meteoric, ornate, orotund,
   ostentatious, overbright, overdone, overelaborate, overinvolved,
   overwrought, pedantic, pompous, pretentious, rakish, raw,
   rhetorical, screaming, sensational, sensationalistic, sententious,
   shallow, showy, shrieking, skin-deep, slick, snazzy, sonorous,
   sparkling, splashy, splurgy, sporty, stilted, superficial, surface,
   tacky, tall, tasteless, tawdry, thin, tinsel, tortuous, vulgar