The Rink at Rockefeller Center is 70 years old today. The rink, in the heart of Midtown and unrivaled for many years (until the Bryant Park's Pond opened), first opened on Christmas Day in 1936. Being located right by the Rockefeller Christmas Tree and the Today Show studios has helped its popularity. It seems to be open today - here are more details.
There are also skating options nearby - there's Bryant Park's Pond and Wollman Rink in Central Park. Rockefeller Center's rink is the smallest and most expensive ($17.50 for adults, not including skate rental); Bryant Park's Pond is free (not including skate rental) and is twice the size of Rock Center; and Wollman Rink is $12 (not including rental) and twice as big as the Pond, four times bigger than Rock Center.
Photograph of the Rockefeller Center Ice Rink by ultraclay! on Flickr