While I was traveling from Buffalo to Pittsburgh, it came to light that another speaker had never seen Niagara Falls! Well!
Should you ever be in Buffalo, the trip to Niagara is a mere 20 minutes, and it's easy in, easy out. The highway will spit you right out into the parking lot, and if you get there early, you may even be able to park right by the pathway entrance, as we did.
The American falls are only a 7 minute stroll into the park. You can walk over to the Canada side via footbridge. The signs as to whether a passport are not required were vague. They basically said that U.S. citizens should be able to get back with photo ID and supporting documents, but frankly, I don't walk around with my birth certificate in my pocket, so I guess it's time to get a passport if I wish to visit my neighbors to the north.
From the Canada site:
If you are a citizen of the United States, you do not need a passport to enter Canada. However, you should carry proof of your citizenship, such as a birth certificate, certificate of citizenship or naturalization, as well as a photo ID. If you are a permanent resident of the U.S., you should bring your Permanent Resident Card (i.e. green card) with you.
Get a passport.
Parking is only $10, and a ticket for all the of special tour options was under $50. We just walked in to visit the falls and headed out again. Given how quickly I got to Buffalo (3 hours) if I ever need to just get away for two days and do something fun and simple, I may zip over to Niagara and do all those silly things I've never done, like the Maid of the Mist boat tour.
The people watching options are endless, so while going with a friend would be optimal, going alone would be fun as well.