The Collaborative International Dictionary of English v.0.48:

Shabby \Shab"by\, a. [Compar. Shabbier; superl. Shabbiest.]
   [See Shab, n., Scabby, and Scab.]
   1. Torn or worn to rage; poor; mean; ragged.
      [1913 Webster]

            Wearing shabby coats and dirty shirts. --Macaulay.
      [1913 Webster]

   2. Clothed with ragged, much worn, or soiled garments. "The
      dean was so shabby." --Swift.
      [1913 Webster]

   3. Mean; paltry; despicable; as, shabby treatment. "Very
      shabby fellows." --Clarendon.
      [1913 Webster]

WordNet (r) 3.0 (2006):

shabby
    adj 1: showing signs of wear and tear; "a ratty old overcoat";
           "shabby furniture"; "an old house with dirty windows and
           tatty curtains" [syn: moth-eaten, ratty, shabby,
           tatty]
    2: mean and unworthy and despicable; "shabby treatment"

Moby Thesaurus II by Grady Ward, 1.0:

283 Moby Thesaurus words for "shabby":
   Mickey Mouse, NG, abandoned, abject, abominable, arrant, atrocious,
   awful, bare, base, battered, beastly, beat-up, bedraggled,
   beggarly, beneath contempt, blameworthy, blowzy, broken-down,
   brutal, budget, careless, cheap, cheesy, chintzy, coarse, common,
   contemptible, contemptuous, crummy, debased, decaying, decrepit,
   deficient, degraded, demeaning, deplorable, depraved, desolate,
   despicable, deteriorated, deteriorating, detestable, dilapidated,
   dingy, dire, dirty, disagreeable, discreditable, disfigured,
   disgraceful, disgusting, dishonorable, disreputable, dog-eared,
   dowdy, down-at-heel, down-at-the-heels, drabbletailed, draggled,
   draggletailed, dreadful, easy, economic, economy, egregious,
   enormous, execrable, faded, fetid, filthy, flagrant, foul,
   fourth-class, frayed, frazzled, frowzy, frugal, frumpish, frumpy,
   full of holes, fulsome, gaudy, gimcracky, good-for-naught,
   good-for-nothing, grave, grievous, gross, grubby, grudging, grungy,
   hateful, heinous, holey, horrible, horrid, ignoble, ignominious,
   imperfect, impolite, in rags, in shreds, in tatters, inadequate,
   incompetent, inexpensive, infamous, inferior, informal, inglorious,
   insufficient, irregular, junk, junky, lamentable, little,
   loathsome, loose, lousy, low, low-class, low-down, low-grade,
   low-priced, low-quality, low-test, lowly, lumpen, maladroit,
   manageable, mangy, mean, mean-spirited, measly, mediocre,
   meretricious, messy, mingy, miserable, moderate, modest, monstrous,
   moth-eaten, mussy, nasty, nefarious, neglected, negligent, niggard,
   niggardly, no-account, no-good, noisome, nominal, not comparable,
   not in it, not worth having, not worth mentioning, not worthwhile,
   notorious, nugacious, nugatory, obnoxious, odious, offensive,
   opprobrious, out of it, outrageous, outworn, paltry, patchy,
   pathetic, penurious, peremptory, petty, pinchpenny, pitiable,
   pitiful, poky, poor, poverty-stricken, punk, ragged, raggedy,
   ramshackle, rank, ratty, reasonable, regrettable, reprehensible,
   reptilian, repulsive, rickety, rotten, rubbishy, rude, ruined,
   ruinous, run-down, sad, scabby, scandalous, schlock, scraggly,
   scrubby, scruffy, scummy, scurvy, scuzzy, second-best,
   second-class, seedy, sensible, shady, shameful, shattered,
   shocking, shoddy, slack, slatternly, sleazy, slipshod, sloppy,
   slovenly, slumlike, slummy, sluttish, small, sordid, sorry,
   squalid, stingy, tacky, tattered, tatty, terrible, third-class,
   third-rate, threadbare, tinny, tired, token, too bad, torn, trashy,
   trivial, trumpery, tumbledown, two-for-a-cent, two-for-a-penny,
   twopenny, twopenny-halfpenny, unclean, uncouth, unexpensive,
   unfriendly, ungenerous, ungentlemanly, unhelpful, unkempt,
   unladylike, unmentionable, unneat, unpleasant, unrespectable,
   unsightly, unskillful, untidy, unworthy, valueless, vile,
   villainous, within means, woeful, worn, worn out, worn-out, worst,
   worth the money, worthless, wrecked, wretched