Today is election day in Massachusetts, and I had to choose between meh and bad. I voted meh, but not without the obligatory "if only there were a viable third party" mutterings. If it didn't mean throwing my vote away, I might have actually voted for the libertarian candidate (no relation).
Our two party system comes directly from our first past the post, aka winner take all, electoral system. All a candidate needs is a plurality of the vote in order to win the whole shebang: if one person gets 49% of the vote and the next two get 48% and 3%, that first person gets 100% of the prize. This leads to tactical voting for one of only two options, as my example shows. I don't like the Democratic candidate, and I don't like the Republican candidate; but I know that the libertarian candidate doesn't have a shot, so I'm not going to throw my vote away by voting for him. I have to choose between meh and bad.
The other way of holding elections, which is more common in parliamentary systems, is proportional representation off a party list. In those elections, you vote for a party instead of a candidate. Each party has its list of candidates, and if the party wins X percent of the vote, they get to put enough people from their list in office to take up X percent of the available seats. For instance, if there are 100 seats, each party puts up its list of 100 candidates. If a party wins 51% of the vote, it gets to put its top 51 candidates in office. If it wins 5% of the vote, it puts 5 people in office.
Both systems — proportional and winner-take-all — have their pros and cons. Proportional systems take away the tactical element of voting, so people are freer to vote for someone they actually like instead of the lesser of two evils. But they're also unstable, since it's rare for any one party to actually have full control. They also give lots of power to small parties, which are in the enviable position of being able to turn a 49% loss into a 51% win if the right quid pro quo is offered.
Of course, we already have those issues in America. Our de facto requirement for a supermajority gives us instability — or rather gridlock, since we don't have a vote of no confidence — and small factions within parties already hijack national policy: witness the power of the religious right and the left's unions.
So, here's my idea. The United States has a bicameral legislature, but both houses use the same electoral system: first past the post. This makes a lot of sense in the Senate, since every state gets only two senators; it's hard to fill 5% of two. But in the House of Representatives, the more populous states could implement a proportional system. Instead of electing House representatives on a per-district level, states could hold an at-large election with party lists. If the Democrats get 60% of Massachusetts' votes, they put in 6 House reps. If the Republicans get 30%, they get 3 reps. And if the dogged libertarians pull off a measly 10% of the vote, they'll still have their say in DC with their single representative.
This would lead to viable third parties in the House, and that publicity could eventually lead to them having a shot in senatorial and even presidential elections. Better yet, we'd have the pros of both systems: stability and slow movement in the upper chamber (Senate), and fluidity of ideas in the lower chamber (the House). The plurality of voters who aren't fully committed to either the Democratic or Republican party line would be the huge beneficiaries.
As far as I know, states are free to elect House representatives however they please, so this idea wouldn't require any change to the federal Constitution. Granted, I don't see any state actually implementing this, but a guy can dream. Maybe it's something for Massachusetts' next referendum.