That movie wasn't just about showing violent world it was more about a reflection on violence, on its consequences, on punishment and on absolution. It may not be screen-shattering by today standards but it's content is still very relevant today imo. Also you can't expect a film from 70s to be as brutal as modern movie, at the time censorship was still very present, and the movie was so extreme that it had to be withdrawn in the UK. ( http://en.wikipedia.org/wiki/A_Clockwork_Orange_%28film%29#American_censorship ).
At the OP I think 2001, Orange Clockwork and Dr. Strangelove are the best. Also Lolita and Shining are great.
Well the ones who censored Jaws and The Exorcist gravely failed.