i should clarify what i said earlier, even though it's not relevent to this discussion. in oz we have the big two:
labor, which is roughly similar to your democrat
liberal, which approximates your republic
now, it happens that labour is big enough to win on its own. liberal NORMALLY isnt so they form a coalition with the national party (which might be considered a bit left or right of liberal depending on who you talk to), which couldnt possibly win on its own.
since those three have the same outcome, we still consider oz a two party system. there is another party that CAN tip the balance as you say. they then are the 'third party' even though obviously ive just listed four! they are called the democrats (who are a tad to the left of labor), and i will be voting for them when our elections come since their policy is more in keeping with what i want for our country.
anyway, IS there a third alternative in the US this time around? a genuine one that isnt fly by night? (our democrats were formed in the seventies by an ex liberal. their stated aim was 'to keep the ---daisies--- honest' !! which i like...