Irresversible was on the very edge - not often you are forced to watch a brutal rape, in ONE scene, for 10 or 15 minutes. But the rest is not that queezy.
Apart from the documentary "army medicine in vietnam" (neither torture or a movie.Just footage from real-life weapon injuries and surgery) which we had to see in the army, only "men behind the sun" can top it, and in this movie the torture scenes are s-i-c-k. Actually there was real-life torture in this movie, on cats and rats. In one scene you can see a cat beeing eaten alive by hundred of rats - a gruesome scene indeed, and yes its real. Later they pour gazoline on the rats and ignite them..
But for the parts of the film that depicts the torture on the chinese, they are sick and many. Probably best to stay clear of this movie if your not interested in a mashup between war movie and exploitation movie.

I did a thread called Cannibal Holocaust vs. Men Behind The Sun where we talked about the issue of non-simulated animal killings in film (people had a lot of interesting things to say).

An addition to Memorable Torture Scenes:

Philosophy Of A Knife - a brutal 4 hour documentary/art-house/torture-porn film about Unit 731.

Recently saw The Stoning of Soraya M.; at the final act when the 'stoning' part begins it turned out unexpectedly pretty disturbing & brutal.

But is stoning torture? If the defining characteristic of torture is that it's meant to cause pain, yet have the victim survive- and the goal of stoning someone is to kill them, correct?

Stoning with a deadly outcome can be defined as torture imo - If we stick to the definition that describes torture as a way of making someone tell you something you want to hear, the whole stoning process is to make the victim beg for his life, confess sins etc. As well as set an example for the rest of the society. Wheter victim dies or lives may be of no concerne. But stoning as a penalty has/is beeing exercised different, with different purposes, and one of the purposes is to kill...
Anyway thats my interpretation of torture and stoning

oh yes, sorry...you got it correct. Stoning isn't a torture at all actually...by "rule/law" continue it until 'the sinner' dies. So by definition it can't be categorized as torture of course except a method of punishment to kill the 'sinner' who committed one of the extreme level of sins & which is adultery.
The reason I put it here when it starts in that film some way it looked like kind of a hideous torture to me at some point but yes at the end it's not remains a torture at all. One of the most ferocious ways of killing people brutally is stoning..we can say.

If only that were true. Read the book: What A Way To Go by Geoffrey Abbott, a fascinating little book about methods of torture and execution. Off the top of my head, methods that were especially gruesome:
Brazen Bull
Cauldron
Scaphismus (incredibly gruesome!)
Spanish Donkey
and many others

It never ceases to amaze me what people are capable of doing to each other.

Yes - Stoning in certain cultures, cultures that practices sharia, they follow rules, and like you said, continue it until 'the sinner' dies. I read somewhere it is very important that, “… no stone should be thrown that should kill with the first or second blow, or so small as a pebble to do no injury to the condemned.
Having problems confirming that rule, but stoning isnt a precise science(?), and when we talk about stoning here i guess we are thinking of capital punishment in the sharia system. But stoning has been reported from Yodok concentration camp in north korea and im not quite sure if death penalty is the motive there, i suspect the torturing element is the key factor there.
They made a documentary about that camp --> http://www.imdb.com/title/tt1266731/

Anyway, i have a feeling that im deviating from topic here, namely torture scenes in movies :o

Agree.

Thanks to WF & PB, I'll try to check out that book & the film if I get them around here in my locality.

I've recently seen the new Samuel L. Jackson movie "Unthinkable". It's about CIA black-ops' use of torture in the interrogation of terrorism suspects.

It's not really a horror flick, but includes lots of brutal and quite realistic torture scenes. Both Jackson and Michael Sheen (who portrays the suspect) give superb performances.