Right now Nate Silver's projections have the Colorado Senate race between Michael Bennet as the closest in the nation (within half of a percent). No matter whether you think of him as a true liberal or not (I think he is), the more important thing is that he's not Ken Buck, a man who claimed to be more qualified than his female primary opponent because he "doesn't wear high heels" and refused to prosecute an admitted rapist.
We need to get out the vote. I'm currently studying in Quito, Ecuador, so I can't knock on doors, but I've already made 10 calls to Colorado voters and plan to make some more. If I can do it from another hemisphere, you can do it from the states (or any other country you happen to be in). Please take just a few minutes of your time to make some calls for Michael or whichever close race is happening in your state.
(Side note, if you are calling from another country or just don't want to use up your monthly minutes making calls, Google voice lets you call any phone in the US for free)