These links are just a starting point, not all the porn I have. All this porn is legal in the US. The first link is to content that was highly illegal to produce, but downloading the videos is perfectly legal in the US.
The first link come from a Japanese company called Bakky. It is the most fucked up porn I have. Anyway, some people affiliated with the company staged some large gang rapes. They hired people for softcore or gentle hardcore scenes and then had about 30 guys walk in and gangrape them. They beat the women, drowned them in bathtubs and pools, forced them to drink alcohol, and so on.
What makes these vids unique is that they're real. The people who made the videos got arrested. Here is a source to confirm that. If you can't read Japanese, Google Translate will get you the gist.
Here is a link to a torrent of the videos.
There's also a great website called exhentai. It's a huge website and has every fetish imaginable. Getting on it is a bit tricky. If you just go to exhentai.org, you will see a sadpanda. Here's what you do:
You can now visit exhentai.org.
This is not just for fucked up porn, by the way. exhentai also has tons of really cute stuff. However, it can get awfully fucked up. This is a general-purpose resource, so you can find your own porn to be ashamed of rather than just viewing what I'm ashamed of. There is also a wiki with an explanation of the tags. Ignore the ponies. The owners are faggots, but the site is good.
I usually like fairly vanilla hentai. My live action porn is the fucked up stuff. However, you can find huge amounts of violent or disturbing porn on exhentai. Here is just one well-known one (two parts):
http://exhentai.org/g/662154/d5c164c9b6/
http://exhentai.org/g/662160/f4abe60743/
You'll have to find your own favorite tags on that site.