The ice park closed down a week or so ago, but I heard that someone has bought it and is going to re-open it. I'm not sure if that's happened yet.
Definitely Monticello. Also, a stroll around the grounds of the University of Virginia is also nice, and you can go in the Rotunda. If you go to the Special Collections Library (which is within easy walking distance of the Rotunda), there is an original copy of the Declaration of Independence on display. It is one of only twenty-five surviving copies printed on the night of July 4, 1776.
If you want to drive a little further from C'ville (probably about 90 minutes), I can highly recommend Luray Caverns.