I think we still have two but the line is becoming slightly blurred. I think rodney_ws said it well: "dumb and dumber". Please realize this is a generalization; I think there are still some good politicians.
It almost seems like we need to band together and elect a regular Joe. These politicians always have an agenda and never do what they say. We need an intelligent, blue collar, thick skinned individual.
Definately 2 parties. I think Lewis Black puts it best...
"We have 2 political parties. The Republicans, which is the party of bad ideas, and the Democrats, which is the party of no ideas. Now this is how our government works. A Republican Congressman stands up and says 'I have a really $h*tty idea!', and then the Democrat Congressman stands up and says 'And I know how to make it even $h*ttyer!'"
In my view we have 2 distinct parties with 2 distinct histories. If they were two branches of the same tree, we would then have a one party system by definition.
Poll's missing a choice: 0 parties. Choosing a political party in the US is not about beliefs/platforms. It is only about the location you're running for office in. Areas are heavily either conservative/liberal (due to the slicing and dicing of districts begin decided by the winners) and there is no one issue that ALL Democrats are on one side of and ALL Republicans are on one side of.
Also, don't forget the power of the third parties (Libertarian, Green, Conservative, etc.). Anyone of these can step into a race and completely change the outcome, despite having an almost 0% of winning.