Gray Line offers just about every sightseeing tour option and combination you could want. There are bus tours by day and by night that run uptown, downtown, and all around the town, as well as bus combos with Circle Line cruises, helicopter flights, museum entrances, and guided visits of sights. There's no real point to purchasing some combination tours -- you don't need a guide to take you to the Statue of Liberty, and you don't save any money on admission by buying the combo ticket. I've found Gray Line to put a higher premium on accuracy than the other big tour-bus operators, so this is your best bet among the biggies.