flip side

flip side
    n 1: a different aspect of something (especially the opposite
         aspect); "the flip side of your positive qualities
         sometimes get out of control"; "on the flip side of
         partnerships he talked about their competition"
    

25 Moby Thesaurus words for "flip side":
      antipode, antipodes, antipole, antithesis, antonym, contra,
      converse, counter, counterbalance, countercheck, counterpoint,
      counterpoise, counterpole, counterterm, foil, inverse, obverse,
      offset, opposite, opposite number, reverse, setoff, the contrary,
      the other side, vis-a-vis