Rockefeller Center: Of course there'st the tree and the ice skating, but we like the concourse level of the building itself, because it has tons of food options (Two Boots pizza, Pret a Manger), a bookstore, and plenty of corridors to meander around while staying warm.
Grand Central: We could spend days there--from watching the trains come and go, the whispering wall just outside the Oyster Bar, looking up at the magnificent ceiling, grabbing a coffee at Joe's, the food court with so many healthy choices, the clean bathrooms...
ABC Carpet and Home: We like to go test out the $10,000 beds, so we get to kick our feet and relax, and pretend we are rich...then, with our well-rested feet, we walk over to the kids section, which has toys and clothes and accessories that we usually haven't seen before...there is so much to look at, and then we get a coffee and hot chocolate at Le Pain Quotidien. This is a great place to come after you've braved the cold at the nearby Greenmarket.
The Metropolitan Museum: One of the prettiest Christmas trees in the city--you could spend an hour just walking around looking at all the vignettes.
Time Warner Center: If you find yourself at a performance at Lincoln Center, at the Nutcracker let's say, this is a nice place to grab lunch and wander around. There is a Whole Foods in the lower level, which has plenty of counter space and ready-made options. Bouchon Bakery has a fantastic chicken soup, and the most amazing chocolate bouchon dessert. And while the shopping there isn't that great, the kids section at Border's Bookstore is good.