-Fellini's La Strada and La Dolce Vita
-Kieslowski's Colours trilogy are some of the best films of the last two decades, Red is honestly hands down one of most favourite films.
-Kubrick's 2001 and Dr Strangelove
-I liked Godard's Pierrot Le Fou however his other films are way too shallow
-Malick's Days of Heaven is utterly beautiful
-Kobayashi's Human Condition are the greatest war films ever made, it's a shame he's ignored because Full Metal Jacket is a basic rip off of the second one.
-Bergman's films are outstanding, esp Persona and Through a Glass Darkly
-End of Evangelion is one of the most ambitious pieces of Sci Fi of the 20th century for me.
And then there's Hitchcock, Lynch, Kurosawa, Miyazaki etc.
Really anything is a work of art aslong as the Director is honest about his work.