At least, the way our Electoral College works a third party candidate can't win. To back this up you only have to examine the 1992 presidential election. Here's a nifty chart I borrowed from Wikipedia.
So what do you do? You don't like either candidate! Well, did you vote in the primary? For the time being the primary seems to be where you go to vote for who you want to be president and the general election is where you go to vote against who you don't want. And just simply not voting has the same effect as voting third party. If the Republicans who sat home and didn't vote, and the Gary Johnson voters had voted for Romney in 2012 it would have been neck and neck and Romney might have won. Obama would not be president and we'd all be better off. It would seem the two party system and the electoral college go hand in hand. If you don't like your party's candidate the primary is where you go to change that next time. That's where the real fight is. It worked in 1980 and we got 8 years of a great president.