A couple of months ago Nils Gilman had a post on best movies of the 1970s.
For reasons that (1) I'm not altogether sure about, and (2) even if I were, might well be too lazy to spell out, I think the movie from this period that sticks with me the most is Apocalypse Now. I also remember some of the era-defining blockbusters, such as Jaws and Star Wars (the 1977 one), quite well. In the case of Apocalypse, in more recent years I saw 'the director's cut' that was released in theaters, with several scenes restored that were not in the version originally shown.
It just occurred to me, writing this post, that there are several movies from the '70s (early in the decade) that I recall that don't show up on N. Gilman's lists: Patton (1970), MASH (1970), The Andromeda Strain (1971), Cabaret (1972), The Day of the Jackal (1973).
(The Andromeda Strain has a sort of special meaning for me, not because I remember it esp. well -- I don't -- and not because it was a great movie -- it may or may not have been, at this remove I can't say -- but for reasons quite extraneous to the movie that I don't want to get into. Sorry to be cryptic. It's not 'first date' or anything like that.)