Okay, heres a fine one, Im very fond of:

El Topo (1970 / Mexico / Alejandro Jodorowsky)

This has over the years really become a cult object, and though it is today by many considered a classic, its notorious history still hasnt come to an end, as the availability of the film is very limited, and there seem to be various edited versions in screen time and screen size. I saw a widescreen version with washed-out colors, which was a bit cut I believe.
Nevertheless the power and vision of this film came through my 16:9 TV screen and I experienced enough of its magic to glimpse its greatness.
The film was made as an underground project in the Mexico of the late 60s, and had difficulty finding distributors, probably because Jodorowsky had already caused a scandal with his previous film "Fando y Lis" in 1967 which was (reportedly after a notorious run in Mexican cinemas, where numerous fights broke out over it) banned by the Mexican government. This film too has in time become a cult object all over the world, and is available on DVD in the US along with an audio commentary by Jodorowsky himself and a documentary on its making. Though I havent seen it yet myself, I dont think fans of surreal films would be disappointed if they took a chance with it. Because all of this Jodorowsky had difficulties with El Topo, but after John Lennon urged a friend to buy distribution rights, it got a world wide release and was heralded all over the world for its weirdness and strange philosophical take. If one considers a statement by Jodorowsky where he said that he asks of film what most North Americans ask of psychedelic drugs, one can see why the hippie-generation all over the world got enthusiastic about it. But while for example a film like "2001 - A space Odyssey" (which also got a lot of negative press on its original release, and commercial success through stoned audiences) became later regarded as a great cinematic achievement, El Topo hasnt yet gotten the same academic "beatification", for better or for worse.
So a modern viewer commonly approaches it not expecting a demanding work of art, but more something along the lines of 70s pseudo-intellectual Eurotrash, spiced with some gore and sex scenes. 
I must confess, that this was also my own approch, when I borrowed it from a local videostore, but I was soon to be disabused.

The film features Jodorowsky himself as the main character El Topo, a gunslinger in search of himself. At the beginning he has a young son with him, but he leaves him alone in a village after finding a woman who is willing to accompany him on his travels. From this point on things start to go downwards for him, as the woman stirs up his ambitions to become something. On his search for fame and money he becomes more and more unscrupulous killing and torturing people, and even aquiring a second wife. The mission he finds himself on is a mixture of a spiritual search and a killing spree, on which he has to find four master gunmen of the desert (each with a personal philosophical stance) which he wants to defeat. After completing his task (not in an honest way that is), he is left alone in the desert to die by the two women who have apparently bscome a couple. 
After this many a viewer (and critic) would have liked the film to end, but Jodorowsky is more interested in his philosophical vision, and the expression of a humanist view of the world, and adds a final chapter to this film, which is imo crucial for its understanding and the overall quality of the film. In the last part (which is the strongest) El Topo awakes in a cave where he has been worshipped for many years as a saint who is going to rescue the clan of deformed outcasts living there. Felling guilty of his former sins, he starts digging a tunnel, to connect the cave with the outer world, represented by a nearby town. Here Jodorowsky gets deeply allegorical and crafts a pessimistic commentary about the state of things in present day Mexico. Ill only tell, that in the following El Topo encounters his son, and that the union of all people is a task that cant be easily completed. The ending shows a bit hope for the human race as a whole, though it is far away from happy. It personally reminded me of the end of Jean Renoirs "La grande illusion", with whom the director shares his love for the common people and his ambivalent belief in and love of mankind, though both know what horrible things it is capable of.
But above all the films quality rests in its subversive take on film and society, which has put many viewers of, and is also the most responsible factor for the films strange reputation.
Jodorowsky uses elements from all over the world, mixing western and eastern philosophies, using film styles as different as the western and the slapstick comedy (where Jodorowskys knowledge of film history gleams), and dialogues and a use of language that seem to come from everywhere. The use of camera-angles contrasts beautiful panoramas with repulsive stagings of human decadence, and from gore to sex scenes, to a lrelationship between a dwarf and a "normal" person, there seem to be few topics the film doesnt have something to say about. But this eclectisicm isnt just a show-off, but at the very center of the films whole concept.
As a whole the only satisfying comparison I found, would be to Glauber Rochas brazilian masterpiece "Black God, white Devil" (which was - made in 64 - surely a huge influence), with added philosophical grounding.
Jodorowsky has afterwards made only a handful of films (some also classics), but with this film alone he has left an important mark in film history.