Here is an excellent article from Examiner.com defending third party voting. The author is Matthew Reece. I particularly like this gem:
1. Voting for a third party candidate is a wasted vote because the candidate cannot win.
Anyone who claims this is claiming that the election process in America is rigged. Let us set aside the matter of whether this is actually the case and focus narrowly on the claim being made. A person who believes this should be trying to convince people either not to vote at all in protest of a corrupt system or to take up arms to start a second American Revolution, not trying to convince people to vote for Republicans or Democrats.