I would definitely suggest a trip to Niagara Falls by car. On your way to Niagara Falls you can drive along the wine route which takes you through some very nice wine country and Niagara On the Lake. (If you have time you could stay at a B&B and take in a show at the famed Shaw Festival.)
As for touring the falls I would park the car and take one of the airconditioned people mover buses which take you around all the sites which saves you time and money. Just a few things you might want to stop at are Maid of the Mist, Butterly Conservatory, and perhaps if you like gambling the Casino.
If you are looking to a quick trip into the US you could cross and go to Goat Falls which is the US side of Niagara Falls and while in the area I would suggest also lunching on Buffalo Chicken Wings. They are certainly unique and quite good. Several years ago I had some Italian friends with me when I crossed the border and all they had to do was have a Temporary Visa signed which was a matter of 5 minutes. Again that was before 9/11.
If you have some specific questions about the area let me know I would happy to answer them. Here are some helpful websites:
Regardless of where you go have a great trip.
Tom, London, Canada