Here's a few less spectacular, but easy to get to:
Beede Falls just off of the Sandwich Notch road in Sandwich. It's in the AMC guide.
There's 2 others, although smaller are worth mentioning because of their location in Stratfford NH, and are relatively unknown. They are at their peak in spring of course, but after a good rainfall they have alot of water going over them. Good trout fishing, too They are on the Big River and known locally as Little and Big Niagra. The nearest that I can tell from Google Earth, the Lat/Lon are: 43 19'33.98"N 71 09'66"W and 43 19'11.76"N 71 09" 57.2"W respectively. Enjoy!
Veni, Vidi, Velcro — I came, I saw, I stuck around