Niagara Falls

Niagara Falls is a large and spectacular series of waterfalls located along the border of New York State and the Canadian province of Ontario. If you want all the fiddly technical details, go check out the relevant article on The Other Wiki. In popular culture, the falls are best known for three things:

Being a destination for honeymooning couples, who dress up in full rain-gear, go out in tour boats and get drenched by the spray.
Idiots/Thrill-seekers going over them in some sort of reinforced barrel.
Monumental Damage, where the falls are under (usually joking) threat of being destroyed/frozen/diverted.

If the falls appear in any sort of comedy or adventure context, someone's going over them, with or without a barrel.

Often suffers from Television Geography.

And if you're wondering about going there as a tourist destination, please make sure you're on the Canadian side of the border. The American side is a Thriving Ghost Town, due to Canada having a much better view of the falls and high-rise casinos.

Appearances in popular culture:

Anime

Featured in one episode of Dinosaur King.

Comedy

The falls is often the MacGuffin in a classic comedy routine done by many performers, including Abbott and Costello and The Three Stooges: a deranged man retells how he finally tracked down the one who wronged him at.. "NIAGARA FALLS!! Slowly I turned.. step by step..."
- Which is made doubly hilarious (at least in the Stooges version) in that he meets the one who wronged him at the end of the bit... only to greet him as an old pal and say that they'd buried the hatchet a long time ago. Cue Niagara Falls, and both of them start up for the beating.

Comics

In one EC Comic story, "Ulric the Undying" jumps over the Falls.
One of hero Tom Strong's enemies dies by falling off the Falls.
In some versions of the Buck Rogers franchise, Earth's capital city is located at Niagara and/or Buck has his headquarters behind the actual falls.
One Captain Marvel story has Dr. Sivana plot to destroy the Falls with a barrel full of explosives. He leaves the scene for a moment, when Ibac the Terrible rushes onto it, on the run from an Abhorrent Admirer. Ibac sees the barrel, dumps the explosives, and stuffs himself inside, at which point Sivana comes back and, unaware of the switch, dumps the barrel (And the unaware of the plot Ibac) into the water over the Falls. Ibac is rescued by the police, who think he's one of those daredevil nuts who try to go over the Falls in a barrel, to which Ibac dizzily responds, "Is that what I've been doing?"

Film

Niagara, obviously.
In Superman 2, Lois Lane jumps into the falls in an attempt to force Clark Kent to prove he's Superman after he saves a kid from falling in.
In Falling Angels, one character's backstory involves dropping her baby off the falls.
John Candy's character in Canadian Bacon is a sheriff near the Falls.
In Peter Jackson's The Fellowship of the Ring the shot of Boromir's boat going over the Falls of Rauros is not CGI - it's actually a stock aerial shot of Niagara with a CGI boat added (over footage of a barrel, if the audio commentary is to be believed).

Literature

Mark Twain's Excerpts From Adam's Diary has Eve naming the Falls "Niagara Falls" because they looked like Niagara Falls.
Charles Dickens goes there in his "American Notes".
Lake Erie and the Niagara Falls are the setting of a chase scene in Jules Verne's novel Master Of The World.

Live Action TV

The short-lived fantasy series Wonderfalls is set at the falls. And yes, there is a barrel episode.
The Office has had a wedding staged there.
The B Plot of Degrassi Takes Manhattan had Spinner and Emma get married there.
The short lived Canadian Series Taking The Falls was set on the Canadian side of the falls.

Music

Lydia The Tattooed Lady has "a view" of them somewhere on her body.

Theater

In Arsenic and Old Lace, this is stated to be Mortimer Brewster's honeymoon destination (he even makes joking references to going over them in a barrel). Never does quite make it, though.
In Guys and Dolls, the song "Adelaide's Lament" (about how she hopes to be married to Nathan) contains

When they get on the train for Niagara, and she can hear church bells chime...

Then they get off at Saratoga for the fourteenth time!

Western Animation

One episode of The Simpsons has Marge and Homer go over the Falls.
On The Fairly Odd Parents, Timmy's parents are framed and arrested at the Falls.
A setting in Sons of Butcher.
Ditto for one episode of Total Drama Island.
Included in a trail of destruction in an episode of Ben 10.
The Woody Woodpecker short Niagara Fools.
In Around the World With Willy Fog, Willy Fog and the gang must cross the cold river with their wind sail while fighting the downriver currents to prevent from going down the Falls in order to catch the next train.
In the Futurama episode "Overclockwise", Fry goes over the Falls in a barrel. In a subversion, it is an unsuccessful attempt at deliberately killing himself.