One of my best friends took these Photos. She always wanted to go to Niagara Falls in the winter and see the falls 'frozen'. In '99 she finally made it, though it was not as frozen as it had been a few weeks prior to her visit, it still had some impressive ice around it. (As a side note, the falls itself never freezes, just the river beneath it and the world around it.)
Here are a few pictures she took there this year. Some of them are a little dark, the weather was very cloudy the day she was taking them, but they give you an good idea of what she saw.