WordNet (r) 3.0 (2006):

offbeat
    adj 1: informal terms; strikingly unconventional [syn: far-
           out, kinky, offbeat, quirky, way-out]
    n 1: an unaccented beat (especially the last beat of a measure)
         [syn: upbeat, offbeat]

Moby Thesaurus II by Grady Ward, 1.0:

74 Moby Thesaurus words for "offbeat":
   Bohemian, bar beat, beat, bizarre, breakaway, contrasting, counter,
   deviant, different, disparate, dissimilar, divergent, diverse,
   downbeat, eccentric, far out, freaky, free and easy, fringy,
   hardly like, heretical, heterodox, hippie, idiosyncratic, informal,
   innovative, kinky, maverick, nonuniform, not cricket, not done,
   not kosher, novel, odd, off, original, out, outlandish, outre,
   peculiar, pulsation, pulse, queer, rare, recherche, scarcely like,
   strange, sui generis, throb, unalike, uncommon, unconventional,
   uncustomary, undreamed-of, unexpected, unfamiliar, unfashionable,
   unheard-of, unidentical, unique, unlike, unmatched, unordinary,
   unorthodox, unresembling, unsame, unsimilar, unthought-of, unusual,
   unwonted, upbeat, way out, weird, weirdo