Wake in Fright. I'm not exactly sure of how a Canadian director, Ted Kotcheff, ended up making one of Australian cinema's most important movies, but the film - also known as Outback, made in 1971, and believed lost for many years - is definitely a must-see, for those interested in Australian cinema, 1970's cinema, or in gritty, sweaty, strikingly cinematic dramas about smalltown demoralization and despair. I'm not sure it's the sort of film that I'd ever watch a second time, but it's one that everyone should see once - though it's not particularly pleasant, and may require a fairly hardy filmgoer to take in all it offers.
the Vancity Theatre website about how the film combines elements of "Heart of Darkness, After Hours, and Groundhog Day" - an apt bit of critical cleverness, but one that probably, in comparing the film to two comedies, doesn't really do justice to how ugly it can be. In particular, nastiness-wise, footage of an actual kangaroo hunt was used, which will be upsetting to people with even a passing fondness for animals - you can read more about that on the film's Wikipedia page. But there are familiar faces for cinephiles, like Donald Pleasance and Jack Thompson, and Kotcheff's choices as director are often inspired and highly cinematic; if he made a better film (he's also noted for First Blood and for what I remember as being a well-acted cult deprogramming film called Split Image) I haven't seen it.