EricAndreychek blogged that the two candidates are very similar and hence a vote either way is insignificant.
While it is true that the parties have been recently centrist, there are still differences between the candidates' platforms, and one should follow a MultiPartyElection algorithm to determine how to cast your vote.
For me, there is one issue above all others: the Doctrine of Preemption. No nation has the right to attack another nation without 1) being attacked, or 2) showing that it is in imminent danger of being attacked. This is similar to the "No Bully" rule in elementary school: you have the right to not get thwacked by other kids unless you're throwing spitballs, putting tape in their hair, etc.
With the power the U.S. has, we must be careful to not be a bully. Comparing our recent Iraq actions with the Cuban Missile Crisis (where we had Very Large Missiles Pointing At Us), our actions then were to embargo Cuba, not to send our troops to Cuba. When we explained why we embargoed Cuba, we had externally verifiable evidence (point your satellite's camera at this lat-long on a sunny day).
In Iraq, we presented evidence of an imminent threat which wasn't verifiable and then we committed our troops. This breaks the "No Bully" rule, and now we're living with the consequences.
To show the rest of the world that we screwed up, and we realize it, we can either [apologize for/reform] the Incredibly Shoddy Intelligence And Decision-Making and/or Depose the Current Executive. We have two bills which aim to reform our intelligence forces. And we have a choice whether we want to Depose the Current Executive or not.
Whether you choose to or not depends on how you value "No Bully" versus the other platform differences between the parties in a MultiPartyElection.