Instant Run-off Voting
I love this idea, and didn't know they are already doing it in San Francisco. Jesse Jackson, Jr. writes in the Boston Globe, via truthout:

With IRV, voters simply rank the candidates in order of preference. If one candidate receives an outright majority of first choice votes, that candidate wins. If there is no majority winner, the rankings are used to conduct a series of instant runoffs until one candidate obtains that majority. In each runoff, the candidate with the lowest vote count is eliminated. If the eliminated candidate is your first choice, your vote is then allocated to your next choice. Voters mark only one ballot, and the final result is a winner supported by a majority of voters.

Our current winner-take-all voting system influences voters to cast their ballots in fear of the candidate they dislike, fostering vitriol from the stump and campaign tactics aimed at personalities not public policy. In contrast, IRV encourages candidates to seek top-choice votes from their supporters and still appeal to their opponents' supporters for second- and third-choice votes. In San Francisco, board of supervisor candidates determined that receiving a majority on the first ballot was unlikely - one district had 22 candidates - so they began to build coalitions with other candidates in an effort to become at least a voter's second choice. This led to substantive discussions of the issues, a feature missing from many campaigns.

I never thought of the benefit to the campaign process, encouraging candidates to be seen together and discuss their similarities. It seems to me this could forge an instant alliance between Democrats and Greens, or Nader, and wipe away the animosity there with one motion. On the negative, this plan adds one more ballot casting, and counting, process to an already troubled system. But, particularly in local races, instant run-offs would save money, encourage more people to run for office, and the first ballot would give us a more accurate picture of the mood of the electorate without the headaches of a parliamentary system.

I am assuming that a state could decide to do this for Presidential elections, that it need not take place on a national level, since states determine how electoral votes are allotted. But I could be wrong.

Would it complicate the voting process that much? Without the threat of wasting a vote, I would not have minded putting Nader first on my ballot, in 2000, and wouldn't have had reason to hate him so much in 2004 that I may have done it again. Who would be against this and why?