The Collaborative International Dictionary of English v.0.48:

Outstanding \Out*stand"ing\, a.
   1. That stands out; undischarged; uncollected; not paid; as,
      outstanding obligations.
      [1913 Webster]

            Revenues . . . as well outstanding as collected.
                                                  --A. Hamilton.
      [1913 Webster]

   2. Conspicuously excellent; markedly superior; distinguished.
      [PJC]

   3. So prominent so as to attract notice; conspicuous; usually
      but not always in a good sense.
      [PJC]

WordNet (r) 3.0 (2006):

outstanding
    adj 1: distinguished from others in excellence; "did outstanding
           work in human relations"; "an outstanding war record"
    2: having a quality that thrusts itself into attention; "an
       outstanding fact of our time is that nations poisoned by anti
       semitism proved less fortunate in regard to their own
       freedom"; "a new theory is the most prominent feature of the
       book"; "salient traits"; "a spectacular rise in prices"; "a
       striking thing about Picadilly Circus is the statue of Eros
       in the center"; "a striking resemblance between parent and
       child" [syn: outstanding, prominent, salient,
       spectacular, striking]
    3: owed as a debt; "outstanding bills"; "the amount still owed";
       "undischarged debts" [syn: outstanding, owing(p),
       undischarged]
    4: of major significance or importance; "a great work of art";
       "Einstein was one of the outstanding figures of the 20th
       centurey" [syn: great, outstanding]

Moby Thesaurus II by Grady Ward, 1.0:

171 Moby Thesaurus words for "outstanding":
   a cut above, above, ahead, appalling, apparent, arrant, arresting,
   ascendant, astonishing, back, better, blatant, bold, capital,
   capping, celebrated, choice, chosen, consequential, conspicuous,
   cortical, distinguished, dominant, due, eclipsing, egregious,
   eminent, emissile, epidermic, esteemed, estimable, exceeding,
   excellent, excelling, exceptional, excrescent, excrescential,
   exomorphic, exterior, external, extraordinary, extrinsic,
   extruding, fabulous, famed, famous, fantastic, finer, first-class,
   first-rate, flagrant, formidable, fringe, glaring, greater,
   hanging out, higher, important, in arrear, in arrears,
   in ascendancy, in relief, in the ascendant, in the foreground,
   in the limelight, incredible, jutting, left, leftover, magnificent,
   main, major, marked, marvelous, mature, memorable, net, noble,
   notable, noted, noteworthy, noticeable, notorious, obtrusive, odd,
   of choice, of mark, one up on, open, ostensible, out, outer,
   outermost, outlying, outmost, outside, outward, outward-facing,
   over, overdue, owed, owing, payable, peripheral, predominant,
   preeminent, prestigious, principal, prognathous, projecting,
   prominent, pronounced, protrudent, protruding, protrusile,
   protrusive, protuberant, protuberating, public, rare, receivable,
   redeemable, remaining, remanent, remarkable, rememberable,
   renowned, reputable, rivaling, roundabout, salient, seeming,
   sensational, signal, significant, smashing, spare, special, star,
   staring, stark-staring, stellar, sticking out, striking, super,
   superb, superexcellent, superficial, superfluous, superior,
   superlative, surface, surpassing, surplus, surviving, telling,
   to spare, to the front, topping, transcendent, transcendental,
   transcending, uncommon, unconsumed, unforgettable, unpaid,
   unresolved, unsettled, unused, upper, wonderful