I prefer a negative vote option.

Basically, you still have only one vote, but you can use that to cast a negative vote against a candidate, rather than a positive one for a candidate.

It's the simplest way to break the monopoly of two parties because a negative vote against a major candidate has the exact same practical effect as a positive vote, but without perpetuating the two-party system. Best of all, those who are afraid of change can vote with a positive vote in exactly the same way they have in the past, with the same effect.