Poster beginnings, 1896 to 1920, please help this chart grow!
The very first "movie posters" appeared at the same time movies were first made, around 1896. They were small posters with a vertical format, advertising the machines and the process, rather than individual movies!
Here are more important milestones in the history of movie posters (I am just writing these off the "top of my head", and I welcome any additions or corrections):
c.1898 - what is believed to be the first poster for a specific movie is seen, for the comedy short "Watering the Gardener"
c.1904 - the first traditional one-sheets for single movies appear
c.1909 - the first one-sheets with actors billed appear
c.1909 - the first exhibitor magazines appear
c.1910 - the first three-sheets appear (printed on 3 one-sheet sized pieces, hence the name)
c.1912 - the first 8x10 stills appear
c.1913 - the first six-sheets appear (printed on 6 one-sheet sized pieces, hence the name)
c.1913 - the first 14x22 window cards appear
c.1914 - the first souvenir program books appear
c.1915 - the first 11x14 lobby cards appear (the very first ones are vertically oriented)
c.1916 - the first pressbooks appear
c.1917 - the first 22x28 half-sheets (called "displays") appear
c.1920 - the first 14x36 inserts appear
c.1920 - the first 24-sheets appear (printed on 24 one-sheet sized pieces, hence the name)
c.1920 - the first studio yearbooks (also called "campaign books") appear
... to be continued!
ATTENTION ALL YOU POSTER HISTORY BUFFS! As I said above, the above chart was created in minutes, and I welcome any additions or corrections. I would LOVE to greatly expand it, and I would especially like to add similar dates for every movie poster producing country! Please email us if you have information to help make this a reality!
HAS unrestored and unenhanced images - IS eMoviePoster.com
HAS 100% honest condition descriptions - IS eMoviePoster.com
HAS auctions where the winner is the higher of two real bidders - IS eMoviePoster.com
HAS up to SIXTEEN weeks of "Pay and Hold" to save a fortune on shipping - IS eMoviePoster.com
HAS real customer service before, during and after EVERY auction, and answers all questions - IS eMoviePoster.com
HAS 25% or 26% "buyers premiums" of any kind (but especially the dreadful "$29 or $49 minimum" ones) - NOT eMoviePoster.com
HAS "reserves or starts over $1 - NOT eMoviePoster.com
HAS hidden bidder IDs - NOT eMoviePoster.com
HAS "nosebleed" shipping charges - NOT eMoviePoster.com
HAS inadequate packaging - NOT eMoviePoster.com
HAS no customer service to speak of, before, during and after any auction, and answers almost no questions - NOT eMoviePoster.com

Comments
c 1900 (?) - the first Herald - something cheap like a handbill would be fairly early.
I will run an updated version in a few months.
HAS unrestored and unenhanced images - IS eMoviePoster.com
HAS 100% honest condition descriptions - IS eMoviePoster.com
HAS auctions where the winner is the higher of two real bidders - IS eMoviePoster.com
HAS up to SIXTEEN weeks of "Pay and Hold" to save a fortune on shipping - IS eMoviePoster.com
HAS real customer service before, during and after EVERY auction, and answers all questions - IS eMoviePoster.com
HAS 25% or 26% "buyers premiums" of any kind (but especially the dreadful "$29 or $49 minimum" ones) - NOT eMoviePoster.com
HAS "reserves or starts over $1 - NOT eMoviePoster.com
HAS hidden bidder IDs - NOT eMoviePoster.com
HAS "nosebleed" shipping charges - NOT eMoviePoster.com
HAS inadequate packaging - NOT eMoviePoster.com
HAS no customer service to speak of, before, during and after any auction, and answers almost no questions - NOT eMoviePoster.com