More pre-mid-20th century posters.
I like the posters in this era for their simplicity. Very sparse, little detail, but they really get their point across.
These are from a site called "Dieselpunk" another blog where you might find anything old. A great source for a picture of the past and what the past thought the future would be like.
1920's - plus
Swiss Poster history
Authur Radebaugh:The Bright Future
Radebaugh Bohn Ads etc.