The Collaborative International Dictionary of English v.0.48:

Wily \Wil"y\, a. [Compar. Wilier; superl. Wiliest.] [From
   Wile.]
   Full of wiles, tricks, or stratagems; using craft or
   stratagem to accomplish a purpose; mischievously artful;
   subtle. "Wily and wise." --Chaucer. "The wily snake."
   --Milton.
   [1913 Webster]

         This false, wily, doubling disposition of mind.
                                                  --South.
   [1913 Webster]

   Syn: Cunning; artful; sly; crafty. See Cunning.
        [1913 Webster]

WordNet (r) 3.0 (2006):

wily
    adj 1: marked by skill in deception; "cunning men often pass for
           wise"; "deep political machinations"; "a foxy scheme"; "a
           slick evasive answer"; "sly as a fox"; "tricky Dick"; "a
           wily old attorney" [syn: crafty, cunning, dodgy,
           foxy, guileful, knavish, slick, sly, tricksy,
           tricky, wily]

Moby Thesaurus II by Grady Ward, 1.0:

69 Moby Thesaurus words for "wily":
   Byzantine, Machiavellian, Machiavellic, acute, arch, artful,
   astute, cagey, calculating, canny, chiseling, clever, collusive,
   covinous, crafty, cunning, cute, deceitful, deep, deep-laid,
   designing, devious, diplomatic, false, falsehearted, feline,
   finagling, foxy, fraudulent, furtive, guileful, indirect,
   ingenious, insidious, inventive, knowing, pawky, politic, ready,
   resourceful, sagacious, scheming, serpentine, sharp, shifty,
   shrewd, slick, slippery, sly, smooth, snaky, sneaky, sophistical,
   stealthy, strategic, subtile, subtle, supple, surreptitious,
   tactical, treacherous, trickish, tricksy, tricky, two-faced,
   underhand, underhanded, vulpine, wary