everything Stanley Kubrick has ever done.
You sir, have quite the good taste in film.
Here is a rough idea of what my list would look like, with some explanations on why I believe people must see these films:
City of God - A landmark in all aspects of modern film making. Absolutely stunning in almost every aspect, if you ask me. Possibly the most well made film I have ever seen.
A Clockwork Orange - A revolutionary film for it's time. Appreciation for the concepts and quetions it brings up about humans and society is still very relevant in our world today.
Where the Wild Things Are - The key word I will always use for this film is "beauty". If you can stop being a little whiny pissant about the fact that it's based on a 15+ page book (whether or not you liked the book or not, it's irrelevant), you should be able to at least appreciate this film a little bit for it's artistic value. Maybe I'm being a little too pretentious about this one, but there are so many aspects of this film that gets overlooked by those who refuse to appreciate what this film does.
American Beauty - Excellent story telling and character developement. Should be reason enough to watch this wonderfully crafted film.
Pulp Fiction - It's a Tarantino class. If you like ANYTHING this man has done, Pulp Fiction should be without a doubt a must see.
Monty Python & The Holy Grail - A classic. Enough said.
Monty Python & The Meaning of Life - More Monty Python genius, with great amounts of comedy with sprinkles of serious content and questions to ask oneself.
Monty Python & The Life of Brian - Excellent parody of religion. Once again, Monty Python translates into = must see.
The Prestige - Excellent examples of acting and story telling. Brilliant all the way through.
I'll add more soon.