I think A Clockwork Orange aged horribly.
The Shining is awesome even by today's standards.
Really? I don't think any of his films have aged badly.
The world in which A Clockwork Orange takes place isn't impressive anymore. I wouldn't even call the movie violent by today's standards. The prison part is still very great but you still have to go through the rather painful and overlong first part of the movie.
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brutal as modern movie, at the time censorship was still very present, and the movie was so extreme that it had to be withdrawn in the UK.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.