The candidate of the Libertarian Party, former New Mexico governor Gary Johnson, is on the ballot in 47 states. He is in court fighting to get on the remaining three: Oklahoma, Pennsylvania, and Michigan. Johnson is not expected to win any state or even get 10% of the vote in any state, but he could pull 1-2% from Romney in states like Colorado and New Hampshire and possibly tip the states to Obama.
Third-party candidates always poll much better than they actually do. When called by a pollster, people who support Johnson are happy to announce their support since it helps their candidate and costs nothing. But when they are in the voting booth they have to decide whether a protest vote is really worth helping the candidate they hate win. Usually they come down for the lesser of two evils and don't make a protest vote.
Libertarians are fairly consistently for freedom from government, so they don't fit the modern left-right axis well. They are against taxes and government regulation of business, but are also against laws prohibiting abortions and the use of marijuana for the same reasons: it's none of the government's business. Nevertheless, Republicans dissatisfied with Romney are more likely to see him as a suitable protest vote than Democrats unhappy with Obama. The party's Website is
www.lp.org, where a small quiz is offered so you can see if you are actually a Libertarian without realizing it.
Link to www.electoral-vote.com