I could rant about the party system in general, which many of our founding fathers warned against, but I'm going to try and restrain myself and focus on why none of the parties offer me anything.
There are two main parties in the US, as I'm sure most of you already know: The Democratic Party (D, dem), and the Republican Party (R, GOP). Now, aside from the fact that calling your party the "Grand Old Party" makes me want to gag myself with a spoon, the main problem I have with both of these "mainstream" parties is that over the years they have been united in selling off our personal liberties to the highest bidder. Both have economic views and plans that will, at the least, not drive our economy into the sea, however I do not appreciate voting for someone who will continue to enslave me. On the flip side are our third parties, the Libertarians, Greens, Reform and others. The problem with them is that, although both the Libertarians and the Greens will grant me personally liberties, their economic ideas are so far right or left that I fear the whole country would collapse if either gained a significant presence in the House or Senate. So, either form the LiberGreen or Greetarian Party, and I'll vote for you, or have two half-seats, one for liberties and one for the economy. That way you could mix and match your vote of two people to one official seat.
Oh, and as for the Reform Party, for the most part they seem to combine the worst of both worlds.