Niagra is an amazing place! I found the easiest way to see it is to park on the US side and walk across on the bridge and down the Canadian side which gives by far the best views (remember that in 2008 you will be required to have a passport to cross into Canada). It is probably a mile or two in walking, but well worth it. The first two photographs on this page were taken from the bridge looking West. At mid-day from the Canadian side you will be photographing south into the sun, so earlier in the morning or later in the evening gives better light. A polarizer on your camera helps take out a lot of the reflections and glare. Also, as you walk closer towards the far falls, the mist becomes a downpour. On a warm summer day it feels good, but have a camera cover for your camera.
As you can see, the Maid of the Mist is still running. There is only one boat on the American side but several from the Canadian side.
On the American side, there is a large structure built out over the river that gives the best view from the American side. This photograph was taken from it. You can take an elevator down to the river and walk up a path to a very close up view looking up at the falls from it's base. There are free raincoats. The cost to look at the view and take the elevator was just a dollar.
On the bottom-center of this picture you can see the path you can take, and some people with their raincoats on.