In most states, the deadline to register to vote by mail has recently passed (see http://www.eac.gov/voter/docs/state-reg-deadlines.xls/attachment_download/file) but the deadline to register is yet to come in Alabama, California, Connecticut, Delaware, Idaho* (mail-in today!), Iowa*, Kansas, Maine*, Maryland, Massachusetts, Minnesota*, Nebraska, Nevada (mail-in has passed but you can still walk in and register), New Hampshire*, New Jersey, New York (today!), North Carolina (mail-in today or at one-stop stations until Nov 1), Oklahoma (mail-in today!), Oregon, South Dakota, Utah (walk-in), Vermont, Washington (walk-in), West Virginia, Wisconsin*, and Guam.
*in starred states you can also register on election day, if you miss the mail-in deadline, which is also true for Montana and Wyoming, whose mail-in deadline has passed. North Dakota does not have voter registration, according to that reference, so I guess North Dakotans just walk in and vote.
Do register, and encourage others around you (or in states mentioned above) to do the same.
Oh, and if you haven't seen it yet, Fake Presidential Candidate Paris Hilton consults with famous fake president Martin Sheen for advice on her ongoing campaign platform.