The Collaborative International Dictionary of English v.0.48:

goofy \goofy\ adj.
   foolish and silly, or appearing silly; as, he wore a goofy
   hat.

   Syn: cockamamie, cockamamy, fool(prenominal), sappy, silly,
        wacky, zany, unreasonable.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

goofy
    adj 1: ludicrous, foolish; "gave me a cockamamie reason for not
           going"; "wore a goofy hat"; "a silly idea"; "some wacky
           plan for selling more books" [syn: cockamamie,
           cockamamy, goofy, sappy, silly, wacky,
           whacky, zany]
    n 1: a cartoon character created by Walt Disney

Moby Thesaurus II by Grady Ward, 1.0:

79 Moby Thesaurus words for "goofy":
   apish, asinine, balmy, bananas, barmy, bats, batty, beany,
   befooled, beguiled, besotted, bonkers, brainless, buffoonish,
   buggy, bughouse, bugs, cockeyed, crackers, crazy, credulous,
   cuckoo, daffy, daft, dazed, dippy, dizzy, doting, dotty, dumb,
   fatuitous, fatuous, flaky, flipped, fond, fool, foolheaded,
   foolish, freaked-out, fruitcakey, fruity, fuddled, futile, gaga,
   gulled, haywire, idiotic, imbecile, inane, inept, infatuated,
   insane, just plain nuts, kooky, loony, loopy, mad, maudlin,
   moronic, nuts, nutty, off the hinges, off the track, off the wall,
   potty, round the bend, sappy, screwball, screwballs, screwy,
   senseless, sentimental, silly, slaphappy, stupid, thoughtless,
   wacky, wet, witless