Sullivan has been asking the question: "Could A Third-Party Candidate Win?"
The short answer is "of course not."
It's impossible without financial resources far beyond the reach of anyone who might have the talent to use them, because a third party candidate must overcome not only the major party candidate but the party backing him or her. And the odds of overcoming the electoral college are astronomical.
Meanwhile, whoever the third party candidate is closer to in terms of platform and ideology would be damaged enough to lose. Run Hillary Clinton as a third party and you damage the president. Run Ron Paul as a third party and you damage the Republican candidate. Furthermore, as we witnessed in 1992, the winning candidate against a strong third party candidate gets elected without a governing mandate.
So unless the electoral system drastically changes, it's impossible. It'll be nice when everyone realizes this and stops daydreaming every four years.