http://www.city-discovery.com/new-york/theme.php?theme=Falls

is one possibility - it is a long way for a day trip.

Hi, we did the trip 2 years ago for my 30th. The actual holiday was through soveriegn so booked the trip separately with them, am at work at the mo but will come back to you later with the exact details. Personally we thought that it was well worth it. We got picked up at 6.30 am and was taken to JFK to catch the flight to buffalo. Once we landed we were greated by our guide. We were taken all round the american falls, where we had lunch provided over looking the falls. We then drove across into canada where we had a further tour which included going underneath Niagra falls. The whole trip was amazing, though it was very long day, it was worth every second.

we went when we stayed in NY and stayed over night. Long journey but well worth thr trip.