The Collaborative International Dictionary of English v.0.48:

Unexcelled \Unexcelled\
   See excelled.

WordNet (r) 3.0 (2006):

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

Moby Thesaurus II by Grady Ward, 1.0:

29 Moby Thesaurus words for "unexcelled":
   beyond compare, beyond comparison, easily first, facile princeps,
   immortal, incomparable, inimitable, invincible, matchless,
   nulli secundus, peerless, second to none, sui generis,
   unapproachable, unapproached, unbeatable, unequaled, unexampled,
   unique, unmatchable, unmatched, unparagoned, unparalleled,
   unpeered, unrivaled, unsurpassable, unsurpassed, without equal,
   without parallel