In terms of voting obligations, I believe that casting your opinion as a member of a democratic society is critical. Even if you don't necessarily like any of the contestants, do some research and decide which is the "lesser evil". Statistically speaking, for example, Democrats in the United States have outnumbered Republicans for almost a century (with one exception that occurred in the early '80s), and yet Democrats have been voted to major political offices roughly about as often as Republicans have been.
Not only are people obligated to simply vote, but also to do research into the people that they are and aren't voting for. Far too many voters vote for the red candidate because he is red, or vice versa. There's nothing wrong with voting for someone of a different party than the one you side with.
Additionally, there is nothing wrong with voting for independents candidates. Although it is true that independents are rarely elected to powerful public office, they should not be looked past. One major reason that independents can never seem to get off the ground is for just the reason that you stated, Genghis, that voters believe that their vote will be a complete waste. The only way that any bipartisan political system will be able to change is if people act as individuals and choose what they truly is right for their society.
