Niagara Falls.... be sure to do the Maid of the Mist boat trip... we went in June and it was super. The butterflies in the conservatory weren't up and about yet so you might wait on that. We did have a room on the Canadian side right above the horseshoe falls on the 15th floor and spent all evening just looking out the window...then they had the fireworks and it was like we were in the middle of them.
NYC -- if you have a chance, take the 4 or 5 hour bus tour...well worth it. They take you around and show you everything! You don't have to worry about getting lost or ran over either. It included a ride on the ferry past the Statute of Liberty and back.
Also there was a ferry we did from I think it was Long Island up to Groton CT or near there...was really cool.
Next time we'll take the time to visit in Norfolk and see some of the shipyards rather than just seeing them from the interstate.
Have a super trip...we loved it when we went there.