This a favorite long weekend getaway location for us - about 5-6 hours drive from home.
If you like "kitschy" stroll along Clifton Hill and check out the attractions. It really is a lot of fun. The view is better from the Canadian side, but we prefer the Niagara Falls State Park on the US side. You get much closer to the water and feel the fury. If you do Cave of The Winds, don't forget to try the Hurricane Deck. One of the best ways to fell the power of the falls is to have a little bit of the Bridal Falls pounding you on the head.
The cable car across the gorge is kind of fun, but not a "must do", the jet boats are probably a better option (one thing we haven't tried yet). There is a walk along the gorge on the Canadian side that is really impressive. You can't believe how powerful the rapids are until you are a few feet away. The "People Mover" buses are a really great way to get around for a day on the Canadian side.
The area is also very rich in history with several key battles that defined the boundaries of both nations.
There is so much to do there, we keep going back and finding more and more!