Wow, Haven't seen this thread in while, but I have thought of another movie that I think is kind of obscure.
I don't think that this is too obscure to the movie loving crowd, but not too many people know about it since it is an older film, making it obscure in my mind, is Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb.
I would also like to add From Hell. Got some play when it was out, but quickly was forgotten.
I'm also going to add Ichi the Killer. Wow, just wow is all I can say about that movie.
Another movie, that the name is escaping me at the moment, is an 80s Italian horror movie called "At The Gates of Hell" I believe. I bought it when I saw it at a convention with a few of my friends and then researched it, and just like Battle Royale was banned from ever playing America, so was this movie. Truly shocking and gruesome. Real horror.