I've just pre-ordered the "definitive" edition (marketing speak for most complete version available) of Metropolis (Lang 1926) on blu ray with a snazzy metal box and assorted other crap. In my opinion one of the most influential movies ever made, and the final word in scope and spectacle in terms of what could be achieved by silent cinema.
M (Lang 1931) is also a masterful piece of cinema and along with Metropolis I feel stands up today, and deserves an audience outside of cinephiles or viewers who can appreciate films primarily due to their importance in terms of the technical nature of cinema and developments in the medium in terms of communicating ideas.
I also like 'Birth of a Nation' (Griffith 1915), perhaps acknowledge its importance in terms of many aspects of cinema would be a better way of phrasing it?