The Collaborative International Dictionary of English v.0.48:

Unsurpassed \Unsurpassed\
   See surpassed.

WordNet (r) 3.0 (2006):

unsurpassed
    adj 1: not capable of being improved on [syn: unexcelled,
           unexceeded, unsurpassed]

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "unsurpassed":
   best, beyond compare, beyond comparison, champion, choice,
   easily first, elect, elite, facile princeps, for the best,
   greatest, handpicked, immortal, incomparable, inimitable,
   invincible, matchless, nulli secundus, optimal, optimum, paramount,
   peerless, picked, prime, prize, quintessential, second to none,
   select, sui generis, supreme, surpassing, unapproachable,
   unapproached, unbeatable, unequaled, unexampled, unexcelled,
   unique, unmatchable, unmatched, unparagoned, unparalleled,
   unpeered, unrivaled, unsurpassable, very best, without equal,
   without parallel