I'm registered, and I do vote-
Lazy options: when you register, you can request to be a permanent absentee- they send you ballots to be mailed in.
Other Ways To Be Heard: I recently signed up for the ALCU's newsletter- they send free faxes for you (in your own words) to your representatives in congress on any civil liberties you feel are being taken away. (ie: the PATRIOT Act).
www.alcu.org
Not to threadjack, but I recommend it - it's easy and takes virtually no time to try to influence your representatives (whether or not you voted for them).