for those of us to the left of center, its been pretty obvious for awhile that the two party system doesn't really work here in the US. The 2000 election showed that a third party candidate can really mess things up.
In 2000, you had Ralph Nader pretty much screw up the election for the Democrats. He had his right to run (free country), but by his running the people that would have voted for Gore over Bush, chose him instead. I think he only won like 1 or 2% of the popular vote, but that was enough to push the favor in Bush's direction.
Now this isn't really the fault of our party system; it's really a flaw in our electoral system.
Instead of using PR (proportional representation) like most of the other democracies of the world, we instead chose to use a form of FPP (first past the post) and the electoral college (bleh Florida, bleh Ohio and their shady Diebold touch screen voting systems that can be hacked).
In FPP, a third party becomes a waste of time. You will never ever get close enough to a majority of people for it to matter.
If we used PR, then the percentage of the vote you received would be the % of seats you hold in Congress. Depending on how you play it, then the leader majority party/coalition (if you don't reach a 50% majority you have to form a coalition gov) becomes the head of state.
So if we had PR in 2000, nader's green party and gore's democratic party would have joined together, formed a coalition government and we wouldn't have any of the questions that sprung up after the 2000 election.
Now, PR doesn't always work. Sometimes people can't see eye to eye (even when they sit on the same side of the political spectrum) and they can't form a coalition gov. One good example of how PR doesn't want to work always is Italy. Anyone that follows world politics, knows that Italy has had problems w/ corruption and just passing normal laws and alot of it has been blamed on their electoral system.
If you want to read more about proportional representation or FPP check out these wiki pages to start you off:Proportional RepresentationFirst Past the Post
and then there are a number of good books on the subject.