Because I have seen very few feature length films before 1920, this will just be a top ten for the decade. Yes, I'm anxious to see enough to get rid of The Birth of a Nation which is horrifically racist -- but, alas, was also hugely influential in terms of the history of cinema and at least when I was hitting college was still always taught in film classes. Unfortunately most films from this era are lost forever.
The Birth of a Nation (1915, DW Griffith)
Intolerance (1916, DW Griffith)
Les Vampires (1915, Louis Feuillade)
Male and Female (1919, Cecil B DeMille)
Stella Maris (1918, Marshall Neilan)