The dealines for registering to vote are different in each state, but in Illinois, the deadline is just 4 weeks away on October 7th, and the rest are quickly approaching.
In order to vote, you must be registered. I do not think that there is any state where you can walk in and register and vote on November 4th. So if you want to vote, you have to get registered now. If you've moved recently, you also need to re-register in your new location.
Voting is a one of our most fundamental rights. Whether you think you really have a voice or whether your vote really matters, it's the system we have and it's not going anywhere soon.
Plus, if you don't get registered and vote, I don't want to hear you whining in 6 months about how much you dislike the new president, senator, governor, dog catcher, etc. As far as I'm concerned, failing to vote means you want no voice and so I give you none.
Don't know where to register? Call your township. You can also register, check to confirm you're registered, and request an absentee ballot right on Barack Obama's website.
In the words of Nike, "Just Do It!"