For anyone in NYC with a car, I just created a Google Calendar for the days when you don't need to move your car. I've added the holidays for the first six months of 2009.
Check the widget out here, and there are links to the Calendar in XML, ICAL and HTML format below the widget:




UPDATE: Tom Karlo has a nice site that lets you know whether alternate side parking rules are in effect at IsAlternateSideParkingInEffect.com