i can second Niagara Falls (grew up in Buffalo), but instead of the Maid of the Mist (which is cool), you need to do the Cave of the Winds trip (takes you within feet of the American Falls)
http://www.niagarafallslive.com/cave_of_the_winds.htm. The other cool thing there is the journey behind the falls (you go into a mine shaft that looks at the backside of the falls from inside the "cliff")
Plus from there you can pop up to Toronto (hour or so away), golf (several courses along the gorge rim), visit Niagara on the Lake, go to a Casino, or continue on to Gettysburg, DC or whatever. If you do head out south from there visit "the Grand Canyon of the East" Letchworth State park...