Time Out New York has a do-it-yourself Gossip Girl Walk with ten stops in midtown Manhattan (keep in mind that the restaurant in The Palace has changed, so you can no longer enjoy the truffled grilled cheese. NYCGo.com has a Gossip Girl Guide to NYC has a run-down of locations based on the show's central characters. If you'd prefer to have a guided Gossip Girl experience in New York City, check out On Location's Gossip Girl Sites! Tour, a three-and-a-half hour bus tour that covers over 40 locations used in filming Gossip Girl.
Photo of Palace Hotel © Heather Cross, licensed to About.com