I suspect that as everyone from an older generation remembered where they were when they heard that President Kennedy had been shot, everyone from my generation will remember how they heard about 9/11. It's been ten years since those terrorist attacks, and it's far too easy to not think about the events of that day. I believe that these attacks were blatantly evil, and we have to remind ourselves of this in order to combat further atrocities from being committed in the future. So in order to recall that there is real evil in the world, here are the videos of the various plane strikes from 9/11. Bear in mind as you watch these that I'm not posting them to satiate anyone's morbid curiosity. You're watching hundreds of people, in the planes and in the buildings, being murdered. So consider that your content warning. Also, if you want to leave a comment espousing some conspiracy theory nonsense, find another website.
American Airlines flight 11
This is the famous and clearest shot of the first plane, filmed by the Naudet brothers, two French documentarians who were filming a documentary on New York firefighters. They completed it, although it became a documentary of 9/11. You can see part 1 here and then follow the links to part 2, 3, etc.
This next one was a webcam, a video art project by Wolfgang Staehle, that took a picture of the Manhattan skyline every second or so from the rooftop of another building. It has a picture of the plane approaching and then immediately after it hit.
Update (September 14, 2015): I've just replaced the video with a better version.
This one is much more difficult to see, so I chose a version that shows it several times and slows it down (just ignore the last 45 seconds of the video). The guy who took this, Pavel Hlava, didn't even realize he had caught the first plane striking the twin towers until months later. After filming this part, he went through a tunnel, and upon emerging he filmed the second plane hitting the towers. So his is the only video that contains both plane hits.
This doesn't show the plane hitting the tower, but you hear it, and then the cameraman shows one of the towers and the smoke plume. It was filmed by a news crew from WNYW in New York.
United Airlines flight 175
After the first plane strike, everyone and their dog were looking up at the twin towers, and those who had video cameras were filming it. Thus the second plane strike was caught by multiple people from multiple angles, and millions of people saw it live on TV. Here's a collection that alleges to be all of the videos made public of the second plane strike.
And this one claims to show all of the plane strikes on the two towers sans sound.
American Airlines flight 77
There is very little video showing the plane that hit the Pentagon, although it was witnessed by hundreds of people. This shows the video taken from a security check-point. Like the Staehle webcam, you only see a snapshot of the plane on the right side of the video at 0:25 and then the explosion.
This next one shows only the relevant portion of the previous video.
And this one shows the same thing from the security check-point one lane over.
This video shows a computer reconstruction of the Pentagon plane strike, which then interposes it on the security video above to show how they match.
And this is a video taken from a hotel that shows the explosion, but not the actual plane. There is a white blur right before the explosion that, at first glance, looks like it could be the plane, but when you look closer, it appears to be a vehicle on the overpass. The plane was going much faster than the vehicle.
United Airlines flight 93
The fourth plane that crashed near Shanksville, Pennsylvania was not caught on film. Up until a few days ago, the photograph below was the only known photo of the smoke plume created when it crashed into a field. This is the plane the passengers tried to take back, and forced the terrorists to crash it before it reached its target (probably either the United States Capitol building or the White House). The passengers may have been able to get control of the cockpit in the last few moments, but they were unable to stop the plane from crashing.
However, just a few days ago a family released a video taken of the smoke plume after the plane crashed. The man who shot it has since passed away, and his family wants to remain anonymous.
While hundreds of people were killed when the planes struck the towers, most of the people who died there died in the subsequent fires, or when they jumped from the towers, or when the buildings collapsed. These were also filmed by multiple cameras and multiple news crews. So the prolificity of such videos is one reason why I'm not going to try to collect them all here.
Another reason is that my point in showing the actual plane strikes (or the immediate aftermath in the case of United 93) is to show the evil of 9/11 and I think that is best exemplified by the free actions of the terrorists who committed it (even though Islamic theology generally denies human free will). The reason I want to show the evil is because I think it must be confronted and stopped rather than glossed over or accommodated, and for obvious reasons, we want to forget the horror of that day. While the videos of the people jumping and of the towers collapsing are horrific, they are results of the original act undertaken by people who chose to align themselves with evil.
The third reason I'm not going to show pictures of people jumping from the towers to their deaths and the towers collapsing is that, frankly, I'm morally exhausted by all of this.