Thinking about it now, maybe the film that affected me the most and i've never been able to watch again is Savior. This film was one of those that hit me out of the blue. I remember renting it thinking it was just another war film, was going through a bit of a war movie kick at the time, it starred Dennis Quaid so never expected anything too amazing.
The movie is based during the bosnian conflict from the point of view of a guy who has run off to join the foreign legion after a revenge attack on a mosque following his wife being killed in a terrorist bombing. Now, the first 15 minutes is pretty hard going in itself but when you finally start to see the atrocities commited during this war...well, i was a gibbering wreck. It made me cry so hard during and maybe for 20-30 minutes after.
I would recommend people watch it so they can get a little education on what happened during the bosnian conflict, i've found upon talking to people in the years since that the knowledge of what went on in these years is sadly lacking a little. I'll put my hands up and say that I was pretty ignorant to it all until this film opened my eyes a little.