A New York institution, led by witty, informed guides (many are also actors), the Circle Line takes travelers round the harbor on cruises of different lengths. The longest makes a complete circle of Manhattan, but I’d recommend the 2-hour "Highlights" cruise instead. You’ll miss Yankee Stadium and the view of the Palisades (the wooded cliffs of New Jersey) on that one, but all of the other highlights—the Statue of Liberty, the lower Manhattan skyline, the Empire State Building, the Chrysler Building—are included. The "city lights" sailing is also lovely; it departs right before sunset, so you’ll see the cityscape in daylight, and then watch it come aglow at night.
Unfortunately, the company recently changed its ticketing policy and now offers to tiers of seating (which makes it harder to game the choice). In order to get the top views, you’ll have to pay more (and because the top seats require climbing stairs, this is not an option for travelers with mobility impairments). Whichever tier of pricing you pick, try and sit on the right side of the boat, facing inward as you enter (that’s the side that faces Manhattan; ask the staff if you’re unclear). It can get very chilly on the water, so be sure to dress in layers, or take a seat inside.
In addition, a number of adults-only live music and DJ cruises sail regularly from the seaport from May through September ($20–$40 per person). Depending on the night of the week, you can groove to the sounds of jazz, Latin, gospel, dance tunes, or blues as you sail along viewing the skyline. The company also runs The Beast, a speedboat tour of the island that kids enjoy.