The Collaborative International Dictionary of English v.0.48:

Cheeky \Cheek"y\,
   a Brazen-faced; impudent; bold. [Slang.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

cheeky
    adj 1: offensively bold; "a brash newcomer disputed the age-old
           rules for admission to the club"; "a nervy thing to say"
           [syn: brash, cheeky, nervy]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "cheeky":
   arrogant, audacious, biggety, bluff, bold, brash, brassy, brazen,
   bumptious, challenging, chutzpadik, cocky, contemptuous, crusty,
   daring, defiant, defying, derisive, disdainful, disregardful,
   disrespectful, facy, flip, flippant, forward, fresh, gally,
   gratuitous, greatly daring, impertinent, impudent, insolent,
   malapert, nervy, pert, regardless of consequences, rude, sassy,
   saucy, smart, smart-alecky, smart-ass, uncalled-for, uncivil,
   wise-ass