The Collaborative International Dictionary of English v.0.48:

Bizarre \Bi*zarre"\, a. [F. bizarre odd, fr. Sp. bizarro
   gallant, brave, liberal, prob. of Basque origin; cf. Basque
   bizarra beard, whence the meaning manly, brave.]
   Odd in manner or appearance; fantastic; whimsical;
   extravagant; grotesque. --C. Kingsley.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bizarre
    adj 1: conspicuously or grossly unconventional or unusual;
           "restaurants of bizarre design--one like a hat, another
           like a rabbit"; "famed for his eccentric spelling"; "a
           freakish combination of styles"; "his off-the-wall
           antics"; "the outlandish clothes of teenagers"; "outre
           and affected stage antics" [syn: bizarre, eccentric,
           freakish, freaky, flaky, flakey, gonzo, off-
           the-wall, outlandish, outre]

Moby Thesaurus II by Grady Ward, 1.0:

83 Moby Thesaurus words for "bizarre":
   Gothic, absurd, amusing, antic, awe-inspiring, awesome, awful,
   awing, baroque, beyond belief, brain-born, cockamamie, crazy,
   curious, deformed, deviant, dream-built, droll, eccentric, eerie,
   erratic, extravagant, fanciful, fancy-born, fancy-built,
   fancy-woven, fantasque, fantastic, florid, foolish, freak,
   freakish, funny, grotesque, high-flown, hilarious, humorous,
   incongruous, incredible, irregular, kinky, laughable, ludicrous,
   maggoty, malformed, misbegotten, misshapen, monstrous, mysterious,
   nonconforming, nonconformist, nonsensical, notional, numinous, odd,
   oddball, offbeat, outlandish, outrageous, outre, peculiar,
   poppycockish, preposterous, priceless, quaint, queer, quizzical,
   rich, ridiculous, risible, rococo, screaming, singular, strange,
   teratogenic, teratoid, uncanny, unconventional, unusual, weird,
   whimsical, wild, witty